28 U.S.C. § 132: Creation and composition of district courts

There shall be in each judicial district a district court which shall be a court of record known as the United States District Court for the district. Each district court shall consist of the district judge or judges for the district in regular active service. Justices or judges designated or assigned shall be competent to sit as judges of the court. Except as otherwise provided by law, or rule or order of court, the judicial power of a district court with respect to any action, suit or proceeding may be exercised by a single judge, who may preside alone and hold a regular or special session of court at the same time other sessions are held by other judges.