Patricia Alves, a federal prisoner, filed a 28 U.S.C. § 2241 (1988) motion challenging the United States Parole Commission's decision to deny her parole until she served fifty-two months of her sentence. Because substantive decisions to grant or deny parole are within the unreviewable discretion of the Parole Commission, we are without the power to engage in judicial review of that decision so long as the Commission's decision was not arbitrary and capricious. Garcia v. Neagle, 660 F.2d 983, 988 (4th Cir. 1981), cert. denied, 454 U.S. 1153 (1982). Only those claims alleging that the agency violated constitutional, statutory, regulatory or other restrictions are reviewable. Id. We agree with the district court that there was a rational basis for Alves's parole denial. Therefore, we affirm the district court's order denying Alves's motion. We dispense with oral argument because the facts and legal contentions are adequately presented in the materials before the Court and argument would not aid the decisional process.