28 U.S.C. § 1651 : US Code - Section 1651: Writs

      (a) The Supreme Court and all courts established by Act of
    Congress may issue all writs necessary or appropriate in aid of
    their respective jurisdictions and agreeable to the usages and
    principles of law.
      (b) An alternative writ or rule nisi may be issued by a justice
    or judge of a court which has jurisdiction.