This case presents the question whether a State, consistently with the Commerce Clause of the Constitution, may impose a nondiscriminatory ad valorem property tax on foreign-owned instrumentalities (cargo containers) of international commerce.

* The facts were "stipulated on appeal," App. 29, and were found by the trial court, id., at 33-36, as follows:

Appellants are six Japanese shipping companies; they are incorporated under the laws of Japan, and they have their principal places of business and commercial domiciles in that country. Id., at 34. Appellants operate vessels used exclusively in foreign commerce; these vessels are registered in Japan and have their home ports there. Ibid. The vessels are specifically designed and constructed to accommodate large cargo shipping containers.1 The containers, like the ships, are owned by appellants, have their home ports in Japan, and are used exclusively for hire in the transportation of cargo in foreign commerce. Id., at 35. Each container is in constant transit save for time spent undergoing repair or awaiting loading and unloading of cargo. All appellants' containers are subject to property tax in Japan and, in fact, are taxed there.

Appellees are political subdivisions of the State of California. Appellants' containers, in the course of their international journeys, pass through appellees' jurisdictions intermittently. Although none of appellants' containers stays permanently in California, some are there at any given time; a container's average stay in the State is less than three weeks. Ibid. The containers engage in no intrastate or interstate transportation of cargo except as continuations of international voyages. Id., at 30. Any movements or periods of nonmovement of containers in appellees' jurisdictions are essential to, and inseparable from, the containers' efficient use as instrumentalities of foreign commerce. Id., at 35-36.

Property present in California on March 1 (the "lien date" under California law) of any year is subject to ad valorem property tax. Cal.Rev. & Tax.Code Ann. §§ 117, 405, 2192 (West 1970 and Supp.1979). A number of appellants' containers were physically present in appellees' jurisdictions on the lien dates in 1970, 1971, and 1972; this number was fairly representative of the containers' "average presence" during each year. App. 35. Appellees levied property taxes in excess of $550,000 on the assessed value of the containers present on March 1 of the three years in question. Id., at 36. During the same period, similar containers owned or controlled by steamship companies domiciled in the United States, that appeared from time to time in Japan during the course of international commerce, were not subject to property taxation in Japan, and therefore were not, in fact, taxed in that country. Id., at 35.

Appellants paid the taxes, so levied, under protest and sued for their refund in the Superior Court for the County of Los Angeles. That court awarded judgment in appellants' favor.2 Id., at 39-40. The court found that appellants' containers were instrumentalities of foreign commerce that had their home ports in Japan where they were taxed. The federal courts, however, in the trial court's view, had "consistently held that vessels which are instrumentalities of foreign commerce and engaged in foreign commerce can be taxed in their home port only." Id., at 24. This rule, said the court, was necessary to avoid multiple taxation, id., at 23; whereas apportionment of taxes can be used to prevent duplicative taxation in interstate commerce, apportionment is "not practical" when one of the taxing entities is a foreign sovereign. In such cases, "[t]here is no tribunal that can adjudicate [competing] rights unless it be the International Court and to invoke its services jurisdiction must be consented to by all parties." Id., at 24. The application of appellees' taxes in derogation of the "home port doctrine," the court concluded, subjected international commerce to multiple taxation and thus was unconstitutional under the Commerce Clause. In so holding, the court followed Scandinavian Airlines System, Inc. v. County of Los Angeles, 56 Cal.2d 11, 14 Cal.Rptr. 25, 363 P.2d 25, cert. denied, 368 U.S. 899, 82 S.Ct. 175, 7 L.Ed.2d 94 (1961) (hereinafter SAS) (ruling that ad valorem property tax levied by California upon aircraft owned, based, and registered abroad and used exclusively in international commerce, was unconstitutional under the Commerce Clause).

The Court of Appeal reversed. 132 Cal.Rptr. 531 (1976). The court appeared to conclude that SAS had been effectively overruled by Sea-Land Service, Inc. v. County of Alameda, 12 Cal.3d 772, 117 Cal.Rptr. 448, 528 P.2d 56 (1974). In Sea-Land, the Supreme Court of California had criticized the home port doctrine and labeled it "anachronistic," and had upheld apportioned property taxation of containers owned by a domestic corporation and used in both intercoastal and foreign commerce. Id., at 787, 117 Cal.Rptr., at 458, 528 P.2d, at 66. The Court of Appeal rejected appellants' arguments that a different result was required here in view of their containers' foreign ownership and exclusively international use. The court likewise dismissed any argument as to multiple taxation. "[T]he possibility of international double taxation of instrumentalities of foreign commerce," it concluded, is "no reason to limit the local power to tax them upon a nondiscriminatory apportioned basis." 132 Cal.Rptr., at 533.3

The California Supreme Court granted a hearing of the case and it, too, reversed the judgment of the Superior Court, essentially adopting the opinion of the Court of Appeal. 20 Cal.3d 180, 141 Cal.Rptr. 905, 571 P.2d 254 (1977). It concluded that "the threat of double taxation from foreign taxing authorities has no role in commerce clause considerations of multiple burdens, since burdens in international commerce are not attributable to discrimination by the taxing state and are matters for international agreement." Id., at 185, 141 Cal.Rptr., at 908, 571 P.2d, at 257. Deeming the containers' foreign ownership and use irrelevant for purposes of constitutional analysis, id., at 186, 141 Cal.Rptr., at 908, 571 P.2d, at 257-258, the court rejected appellants' Commerce Clause challenge and sustained the validity of the tax as applied.4

Appellants appealed. We postponed consideration of our jurisdiction to the hearing on the merits. 436 U.S. 955, 98 S.Ct. 3067, 57 L.Ed.2d 1120 (1978).

This Court has appellate jurisdiction to review a final judgment rendered by the highest court of a State in which a decision could be had "where is drawn in question the validity of a statute of any state on the ground of its being repugnant to the Constitution, treaties or laws of the United States, and the decision is in favor of its validity." 28 U.S.C. § 1257(2). In this case, appellants drew in question the validity of California's ad valorem property tax, contending that the tax, as applied to their containers, was repugnant to the Commerce Clause and various treaties, and the California Supreme Court sustained the validity of the tax. Under these circumstances, this Court's appellate jurisdiction would seem manifest.

Appellees suggest that the California courts did not in reality uphold the tax statute against constitutional attack, but simply refused to extend to appellants a constitutional immunity from taxation. Motion to Dismiss or Affirm 2. Appellees' suggested recharacterization is unpersuasive. Appellants squarely challenged the constitutionality of the tax statute, as applied and the California Supreme Court just as squarely sustained its validity, as applied. We have held consistently that a state statute is sustained within the meaning of § 1257(2) when a state court holds it applicable to a particular set of facts as against the contention that such application is invalid on federal grounds. E. g., Cohen v. California, 403 U.S. 15, 17-18, 91 S.Ct. 1780, 1784, 29 L.Ed.2d 284 (1971); Warren Trading Post v. Arizona Tax Comm'n, 380 U.S. 685, 686, and n. 1, 85 S.Ct. 1242, 1243, 14 L.Ed.2d 165 (1965); Bantam Books, Inc. v. Sullivan, 372 U.S. 58, 61 n. 3, 83 S.Ct. 631, 634, 9 L.Ed.2d 584 (1963); Dahnke-Walker Milling Co. v. Bondurant, 257 U.S. 282, 288-290, 42 S.Ct. 106, 107-108, 66 L.Ed. 239 (1921). We conclude that we have appellate jurisdiction of this case.

The "home port doctrine" was first alluded to in Hays v. Pacific Mail S. S. Co., 17 How. 596, 58 U.S. 596, 15 L.Ed. 254 (1855). In Hays, California sought to impose property taxes on oceangoing vessels intermittently touching its ports. The vessels' home port was New York City, where they were owned, registered, and based; they engaged in intercoastal commerce by way of the Isthmus of Panama, and remained in California briefly to unload cargo and undergo repairs. This Court held that the ships had established no tax situs in California:

"We are satisfied that the State of California had no jurisdiction over these vessels for the purpose of taxation; they were not, properly, abiding within its limits, so as to become incorporated with the other personal property of the State; they were there but temporarily, engaged in lawful trade and commerce, with their situs at the home port, where the vessels belonged, and where the owners were liable to be taxed for the capital invested, and where the taxes had been paid." Id., at 599-600.

Because the vessels were properly taxable in their home port, this Court concluded, they could not be taxed in California at all.5

The "home port doctrine" enunciated in Hays was a corollary of the medieval maxim mobilia sequuntur personam ("movables follow the person," see Black's Law Dictionary 1154 (rev. 4th ed. 1968)) and resulted in personal property being taxable in full at the domicile of the owner. This theory of taxation, of course, has fallen into desuetude, and the "home port doctrine," as a rule for taxation of moving equipment, has yielded to a rule of fair apportionment among the States. This Court, accordingly, has held that various instrumentalities of commerce may be taxed, on a properly apportioned basis, by the nondomiciliary States through which they travel. E. g., Pullman's Palace Car Co. v. Pennsylvania, 141 U.S. 18, 11 S.Ct. 876, 35 L.Ed. 613 (1891); Ott v. Mississippi Valley Barge Line Co., 336 U.S. 169, 69 S.Ct. 432, 93 L.Ed. 585 (1949); Braniff Airways, Inc. v. Nebraska State Bd. of Equalization, 347 U.S. 590, 74 S.Ct. 757, 98 L.Ed. 967 (1954). In discarding the "home port" theory for the theory of apportionment, however, the Court consistently has distinguished the case of oceangoing vessels. E. g., Pullman's Palace, 141 U.S., at 23-24, 11 S.Ct. at 878 (approving apportioned tax on railroad rolling stock, but distinguishing vessels "engaged in interstate or foreign commerce upon the high seas"); Ott, 336 U.S., at 173-174, 69 S.Ct., at 434 (approving apportioned tax on barges navigating inland waterways, but "not reach[ing] the question of taxability of ocean carriage"); Braniff, 347 U.S., at 600, 74 S.Ct., at 763 (approving apportioned tax on domestic aircraft, but distinguishing vessels "used to plow the open seas"). Relying on these cases, appellants argue that the "home port doctrine," yet vital, continues to prescribe the proper rule for state taxation of oceangoing ships. Since containers are "functionally a part of the ship," Leather's Best, Inc. v. S. S. Mormaclynx, 451 F.2d 800, 815 (CA2 1971), appellants conclude, the containers, like the ships, may be taxed only at their home ports in Japan, and thus are immune from tax in California.

Although appellants' argument, as will be seen below, has an inner logic, we decline to cast our analysis of the present case in this mold. The "home port doctrine" can claim no unequivocal constitutional source; in assessing the legitimacy of California's tax, the Hays Court did not rely on the Commerce Clause, nor could it, in 1854, have relied on the Due Process Clause of the Fourteenth Amendment. The basis of the "home port doctrine," rather, was common-law jurisdiction to tax.6 Given its origins, the doctrine could be said to be "anachronistic"; given its underpinnings, it may indeed be said to have been "abandoned." Northwest Airlines, Inc. v. Minnesota, 322 U.S. 292, 320, 64 S.Ct. 950, 964, 88 L.Ed. 1283 (1944) (Stone, C. J., dissenting). As a theoretical matter, then, to rehabilitate the "home port doctrine" as a tool of Commerce Clause analysis would be somewhat odd. More importantly, to hold in this case that the "home port doctrine" survives would be to prove too much. If an oceangoing vessel could indeed be taxed only at its home port, taxation by a nondomiciliary State logically would be barred, regardless of whether the vessel were domestically or foreign owned, and regardless of whether it were engaged in domestic or foreign commerce. In Hays itself, the vessel was owned in New York and was engaged in interstate commerce through international waters. There is no need in this case to decide currently the broad proposition whether mere use of international routes is enough, under the "home port doctrine," to render an instrumentality immune from tax in a nondomiciliary State. The question here is a much more narrow one, that is, whether instrumentalities of commerce that are owned, based, and registered abroad and that are used exclusively in international commerce, may be subjected to apportioned ad valorem property taxation by a State.7

The Constitution provides that "Congress shall have Power . . . To regulate Commerce with foreign Nations, and among the several States, and with the Indian Tribes." Art. I, § 8, cl. 3. In construing Congress' power to "regulate Commerce . . . among the several States," the Court recently has affirmed that the Constitution confers no immunity from state taxation, and that "interstate commerce must bear its fair share of the state tax burden." Washington Revenue Dept. v. Association of Wash. Stevedoring Cos., 435 U.S. 734, 750, 98 S.Ct. 1388, 1399, 55 L.Ed.2d 682 (1978). Instrumentalities of interstate commerce are no exception to this rule, and the Court regularly has sustained property taxes as applied to various forms of transportation equipment. See Pullman's Palace, supra (railroad rolling stock); Ott, supra (barges on inland waterways); Braniff, supra (domestic aircraft). Cf. Central Greyhound Lines v. Mealey, 334 U.S. 653, 663, 68 S.Ct. 1260, 1266, 92 L.Ed. 1633 (1948) (motor vehicles). If the state tax "is applied to an activity with a substantial nexus with the taxing State, is fairly apportioned, does not discriminate against interstate commerce, and is fairly related to the services provided by the State," no impermissible burden on interstate commerce will be found. Complete Auto Transit, Inc. v. Brady, 430 U.S. 274, 279, 97 S.Ct. 1076, 1079, 51 L.Ed.2d 326 (1977); Washington Revenue Dept., 435 U.S., at 750, 98 S.Ct. at 1399.

Appellees contend that cargo shipping containers, like other vehicles of commercial transport, are subject to property taxation, and that the taxes imposed here meet Complete Auto 's fourfold requirements. The containers, they argue, have a "substantial nexus" with California because some of them are present in that State at all times; jurisdiction to tax is based on "the habitual employment of the property within the State," Braniff, 347 U.S., at 601, 74 S.Ct. at 764, and appellants' containers habitually are so employed. The tax, moreover, is "fairly apportioned," since it is levied only on the containers' "average presence" in California.8 The tax "does not discriminate," thirdly, since it falls evenhandedly on all personal property in the State; indeed, as an ad valorem tax of general application, it is of necessity nondiscriminatory. The tax, finally, is "fairly related to the services provided by" California, services that include not only police and fire protection, but also the benefits of a trained work force and the advantages of a civilized society.

These observations are not without force. We may assume that, if the containers at issue here were instrumentalities of purely interstate commerce, Complete Auto would apply and be satisfied, and our Commerce Clause inquiry would be at an end. Appellants' containers, however, are instrumentalities of foreign commerce, both as a matter of fact9 and as a matter of law.10 The premise of appellees' argument is that the Commerce Clause analysis is identical, regardless of whether interstate or foreign commerce is involved. This premise, we have concluded, must be rejected. When construing Congress' power to "regulate Commerce with foreign Nations," a more extensive constitutional inquiry is required.

When a State seeks to tax the instrumentalities of foreign commerce, two additional considerations, beyond those articulated in Complete Auto, come into play. The first is the enhanced risk of multiple taxation. It is a commonplace of constitutional jurisprudence that multiple taxation may well be offensive to the Commerce Clause. E. g., Evco v. Jones, 409 U.S. 91, 94, 93 S.Ct. 349, 351, 34 L.Ed.2d 325 (1972); Central R. Co. v. Pennsylvania, 370 U.S. 607, 612, 82 S.Ct. 1297, 1301, 8 L.Ed.2d 720 (1962); Standard Oil Co. v. Peck, 342 U.S. 382, 384-385, 72 S.Ct. 309, 310, 96 L.Ed. 427 (1952); Ott, 336 U.S., at 174, 69 S.Ct., at 434; J. D. Adams Mfg. Co. v. Storen, 304 U.S. 307, 311, 58 S.Ct. 913, 915, 82 L.Ed. 1365 (1938). In order to prevent multiple taxation of interstate commerce, this Court has required that taxes be apportioned among taxing jurisdictions, so that no instrumentality of commerce is subjected to more than one tax on its full value. The corollary of the apportionment principle, of course, is that no jurisdiction may tax the instrumentality in full. "The rule which permits taxation by two or more states on an apportionment basis precludes taxation of all of the property by the state of the domicile. . . . Otherwise there would be multiple taxation of interstate operations." Standard Oil Co. v. Peck, 342 U.S., at 384-385, 72 S.Ct. at 310; Braniff, 347 U.S., at 601, 74 S.Ct. at 764. The basis for this Court's approval of apportioned property taxation, in other words, has been its ability to enforce full apportionment by all potential taxing bodies.

Yet neither this Court nor this Nation can ensure full apportionment when one of the taxing entities is a foreign sovereign. If an instrumentality of commerce is domiciled abroad, the country of domicile may have the right, consistently with the custom of nations, to impose a tax on its full value.11 If a State should seek to tax the same instrumentality on an apportioned basis, multiple taxation inevitably results. Hence, whereas the fact of apportionment in interstate commerce means that "multiple burdens logically cannot occur," Washington Revenue Dept., 435 U.S., at 746-747, 98 S.Ct. at 1397-98, the same conclusion, as to foreign commerce, logically cannot be drawn. Due to the absence of an authoritative tribunal capable of ensuring that the aggregation of taxes is computed on no more than one full value, a state tax, even though "fairly apportioned" to reflect an instrumentality's presence within the State, may subject foreign commerce " 'to the risk of a double tax burden to which [domestic] commerce is not exposed, and which the commerce clause forbids.' " Evco v. Jones, 409 U.S., at 94, 93 S.Ct. at 351, quoting J. D. Adams Mfg. Co., 304 U.S., at 311, 58 S.Ct. at 915.

Second, a state tax on the instrumentalities of foreign commerce may impair federal uniformity in an area where federal uniformity is essential. Foreign commerce is pre-eminently a matter of national concern. "In international relations and with respect to foreign intercourse and trade the people of the United States act through a single government with unified and adequate national power." Board of Trustees v. United States, 289 U.S. 48, 59, 53 S.Ct. 509, 510, 77 L.Ed. 1025 (1933). Although the Constitution, Art. I, § 8, cl. 3, grants Congress power to regulate commerce "with foreign Nations" and "among the several States" in parallel phrases, there is evidence that the Founders intended the scope of the foreign commerce power to be the greater.12 Cases of this Court, stressing the need for uniformity in treating with other nations, echo this distinction.13 In approving state taxes on the instrumentalities of interstate commerce, the Court consistently has distinguished oceangoing traffic, supra, at 442; these cases reflect an awareness that the taxation of foreign commerce may necessitate a uniform national rule. Indeed, in Pullman's Palace, the Court wrote that the " 'vehicles of commerce by water being instruments of intercommunication with other nations, the regulation of them is assumed by the national legislature.' " 141 U.S., at 24, 11 S.Ct. at 878, quoting Railroad Co. v. Maryland, 21 Wall. 456, 470, 22 L.Ed. 678 (1875). Finally, in discussing the Import-Export Clause, this Court, in Michelin Tire Corp. v. Wages, 423 U.S. 276, 285, 96 S.Ct. 535, 540, 46 L.Ed.2d 495 (1976), spoke of the Framers' overriding concern that "the Federal Government must speak with one voice when regulating commercial relations with foreign governments." The need for federal uniformity is no less paramount in ascertaining the negative implications of Congress' power to "regulate Commerce with foreign Nations" under the Commerce Clause.14

A state tax on instrumentalities of foreign commerce may frustrate the achievement of federal uniformity in several ways. If the State imposes an apportioned tax, international disputes over reconciling apportionment formulae may arise.15 If a novel state tax creates an asymmetry in the international tax structure, foreign nations disadvantaged by the levy may retaliate against American-owned instrumentalities present in their jurisdictions. Such retaliation of necessity would be directed at American transportation equipment in general, not just that of the taxing State, so that the Nation as a whole would suffer.16 If other States followed the taxing State's example, various instrumentalities of commerce could be subjected to varying degrees of multiple taxation, a result that would plainly prevent this Nation from "speaking with one voice" in regulating foreign commerce.

For these reasons, we believe that an inquiry more elaborate than that mandated by Complete Auto is necessary when a State seeks to tax the instrumentalities of foreign, rather than of interstate, commerce. In addition to answering the nexus, apportionment, and nondiscrimination questions posed in Complete Auto, a court must also inquire, first, whether the tax, notwithstanding apportionment, creates a substantial risk of international multiple taxation, and, second, whether the tax prevents the Federal Government from "speaking with one voice when regulating commercial relations with foreign governments." If a state tax contravenes either of these precepts, it is unconstitutional under the Commerce Clause.

Analysis of California's tax under these principles dictates that the tax, as applied to appellants' containers is impermissible. Assuming, arguendo, that the tax passes muster under Complete Auto, it cannot withstand scrutiny under either of the additional tests that a tax on foreign commerce must satisfy.

First, California's tax results in multiple taxation of the instrumentalities of foreign commerce. By stipulation, appellants' containers are owned, based, and registered in Japan; they are used exclusively in international commerce; and they remain outside Japan only so long as needed to complete their international missions. Under these circumstances, Japan has the right and the power to tax the containers in full. California's tax, however, creates more than the risk of multiple taxation; it produces multiple taxation in fact. Appellants' containers not only "are subject to property tax . . . in Japan," App. 32, but, as the trial court found, "are, in fact, taxed in Japan." Id., at 35. Thus, if appellees' levies were sustained, appellants "would be paying a double tax." Id., at 23.17

Second, California's tax prevents this Nation from "speaking with one voice" in regulating foreign trade. The desirability of uniform treatment of containers used exclusively in foreign commerce is evidenced by the Customs Convention on Containers, which the United States and Japan have signed. See n. 10, supra. Under this Convention, containers temporarily imported are admitted free of "all duties and taxes whatsoever chargeable by reason of importation." 20 U.S.T., at 304. The Convention reflects a national policy to remove impediments to the use of containers as "instruments of international traffic." 19 U.S.C. § 1322(a). California's tax, however, will frustrate attainment of federal uniformity. It is stipulated that American-owned containers are not taxed in Japan. App. 35. California's tax thus creates an asymmetry in international maritime taxation operating to Japan's disadvantage. The risk of retaliation by Japan, under these circumstances, is acute, and such retaliation of necessity would be felt by the Nation as a whole.18 If other States follow California's example (Oregon already has done so19), foreign-owned containers will be subjected to various degrees of multiple taxation, depending on which American ports they enter. This result, obviously, would make "speaking with one voice" impossible. California, by its unilateral act, cannot be permitted to place these impediments before this Nation's conduct of its foreign relations and its foreign trade.

Because California's ad valorem tax, as applied to appellants' containers, results in multiple taxation of the instrumentalities of foreign commerce, and because it prevents the Federal Government from "speaking with one voice" in international trade, the tax is inconsistent with Congress' power to "regulate Commerce with foreign Nations." We hold the tax, as applied, unconstitutional under the Commerce Clause.

Appellees proffer several objections to this holding. They contend, first, that any multiple taxation in this case is attributable, not to California, but to Japan. California, they say, is just trying to take its share; it should not be foreclosed by Japan's election to tax the containers in full. California's tax, however, must be evaluated in the realistic framework of the custom of nations. Japan has the right and the power to tax appellants' containers at their full value; nothing could prevent it from doing so. Appellees' argument may have force in the interstate commerce context. Cf. Moorman Mfg. Co. v. Bair, 437 U.S. 267, 277, and n. 12, 98 S.Ct. 2340, 2346, 57 L.Ed.2d 197 (1978). In interstate commerce, if the domiciliary State is "to blame" for exacting an excessive tax, this Court is able to insist upon rationalization of the apportionment. As noted above, however, this Court is powerless to correct malapportionment of taxes imposed from abroad in foreign commerce.

Appellees contend, secondly, that any multiple taxation created by California's tax can be cured by congressional action or by international agreement. We find no merit in this contention. The premise of appellees' argument is that a State is free to impose demonstrable burdens on commerce, so long as Congress has not pre-empted the field by affirmative regulation. But it long has been "accepted constitutional doctrine that the commerce clause, without the aid of Congressional legislation . . . affords some protection from state legislation inimical to the national commerce, and that in such cases, where Congress has not acted, this Court, and not the state legislature, is under the commerce clause the final arbiter of the competing demands of state and national interests." Southern Pacific Co. v. Arizona ex rel. Sullivan, 325 U.S. 761, 769, 65 S.Ct. 1515, 1520, 89 L.Ed. 1915 (1945). Accord, Hughes v. Oklahoma, 441 U.S. 322, 326 and n. 2, 99 S.Ct. 1727, 1731, 60 L.Ed.2d 250 (1979); Boston Stock Exchange v. State Tax Comm'n, 429 U.S. 318, 328, 97 S.Ct. 599, 606, 50 L.Ed.2d 514 (1977). Appellees' argument, moreover, defeats, rather than supports, the cause it aims to promote. For to say that California has created a problem susceptible only of congressional—indeed, only of international—solution is to concede that the taxation of foreign-owned containers is an area where a uniform federal rule is essential. California may not tell this Nation or Japan how to run their foreign policies.

Third, appellees argue that, even if California's tax results in multiple taxation, that fact, after Moorman is insufficient to condemn a state tax under the Commerce Clause. In Moorman, the Court refused to invalidate Iowa's single-factor income tax apportionment formula, even though it posed a credible threat of overlapping taxation because of the use of three-factor formulae by other States. See also the several opinions in Moorman in dissent. 437 U.S., at 281, 282, and 283, 98 S.Ct. at 2348-2349. That case, however, is quite different from this one. In Moorman, the existence of multiple taxation, on the record then before the Court, was "speculative," id., at 276, 98 S.Ct. at 2346; on the record of the present case, multiple taxation is a fact. In Moorman, the problem arose, not from lack of apportionment, but from mathematical imprecision in apportionment formulae. Yet, this Court consistently had held that the Commerce Clause "does not call for mathematical exactness nor for the rigid application of a particular formula; only if the resulting valuation is palpably excessive will it be set aside." Northwest Airlines, Inc. v. Minnesota, 322 U.S., at 325, 64 S.Ct. at 967 (Stone, C. J., dissenting). Accord, Moorman, 437 U.S., at 274, 98 S.Ct. at 2345 (citing cases). See Hellerstein, State Taxation Under the Commerce Clause: An Historical Perspective, 29 Vand.L.Rev. 335, 347 (1976). This case, by contrast, involves no mere mathematical imprecision in apportionment; it involves a situation where true apportionment does not exist and cannot be policed by this Court at all. Moorman, finally, concerned interstate commerce. This case concerns foreign commerce. Even a slight overlapping of tax—a problem that might be deemed de minimis in a domestic context—assumes importance when sensitive matters of foreign relations and national sovereignty are concerned.20

Finally, appellees present policy arguments. If California cannot tax appellants' containers, they complain, the State will lose revenue, even though the containers plainly have a nexus with California; the State will go uncompensated for the services it undeniably renders the containers; and, by exempting appellants' containers from tax, the State in effect will be forced to discriminate against domestic, in favor of foreign, commerce. These arguments are not without weight, and, to the extent appellees cannot recoup the value of their services through user fees, they may indeed be disadvantaged by our decision today. These arguments, however, are directed to the wrong forum. "Whatever subjects of this [the commercial] power are in their nature national, or admit only of one uniform system, or plan of regulation, may justly be said to be of such a nature as to require exclusive legislation by Congress." Cooley v. Board of Wardens, 12 How. 299, 319, 53 U.S. 299, 13 L.Ed. 996 (1852). The problems to which appellees refer are problems that admit only of a federal remedy. They do not admit of a unilateral solution by a State.

The judgment of the Supreme Court of California is reversed.

It is so ordered.

Substantially for the reasons set forth by Justice Manuel in his opinion for the unanimous Supreme Court of California, 20 Cal.3d 180, 141 Cal.Rptr. 905, 571 P.2d 254, Mr. Justice REHNQUIST is of the opinion that the judgment of that court should be affirmed.