5 USC 304 - Subpenas

(a) The head of an Executive department or military department or bureau thereof in which a claim against the United States is pending may apply to a judge or clerk of a court of the United States to issue a subpena for a witness within the jurisdiction of the court to appear at a time and place stated in the subpena before an individual authorized to take depositions to be used in the courts of the United States, to give full and true answers to such written interrogatories and cross-interrogatories as may be submitted with the application, or to be orally examined and cross-examined on the subject of the claim.
(b) If a witness, after being served with a subpena, neglects or refuses to appear, or, appearing, refuses to testify, the judge of the district in which the subpena issued may proceed, on proper process, to enforce obedience to the subpena, or to punish for disobedience, in the same manner as a court of the United States may in case of process of subpena ad testificandum issued by the court.