28 CFR § 2.217 - Issuance of subpoena for appearance of witnesses or production of documents.
(1) If any adverse witness (i.e., a person who has given information upon which revocation may be based) refuses, upon request by the Commission, to appear at a probable cause hearing or local revocation hearing, a Commissioner may issue a subpoena for the appearance of such witness.
(2) In addition, a Commissioner may, upon a showing by the releasee that a witness whose testimony is necessary to the proper disposition of his case will not appear voluntarily at a local revocation hearing or provide an adequate written statement of his testimony, issue a subpoena for the appearance of such witness at the revocation hearing.
(3) A subpoena may also be issued at the discretion of a Commissioner if an adverse witness is judged unlikely to appear as requested, or if the subpoena is deemed necessary for the orderly processing of the case.
(b) A subpoena may require the production of documents as well as, or in lieu of, a personal appearance. The subpoena shall specify the time and the place at which the person named therein is commanded to appear, and shall specify any documents required to be produced.
(c) A subpoena may be served by any Federal or District of Columbia officer authorized to serve criminal process. The subpoena may be served at any place within the judicial district in which the place specified in the subpoena is located, or any place where the witness may be found. Service of a subpoena upon a person named therein shall be made by delivering a copy of the subpoena to such a person.
(d) If a person refuses to obey such subpoena, the Commission may petition a court of the United States for the judicial district in which the revocation proceeding is being conducted, or in which such person may be found, to require such person to appear, testify, or produce evidence. If the court issues an order requiring such person to appear before the Commission, failure to obey such an order is punishable as contempt, as provided in 18 U.S.C. 4214(a)(2).