49 CFR § 386.53 - Subpoenas, witness fees.
(a) Applications for the issuance of subpoenas must be submitted to the Assistant Administrator, or in cases that have been called for a hearing, to the administrative law judge. The application must show the general relevance and reasonable scope of the evidence sought. Any person served with a subpoena may, within 7 days after service, file a motion to quash or modify. The motion must be filed with the official who approved the subpoena. The filing of a motion shall stay the effect of the subpoena until a decision is reached.
(b) Witnesses shall be entitled to the same fees and mileage as are paid witnesses in the courts of the United States. The fees shall be paid by the party at whose instance the witness is subpoenaed or appears.
(c) Paragraph (a) of this section shall not apply to the Administrator or employees of the FMCSA or to the production of documents in their custody. Applications for the attendance of such persons or the production of such documents at a hearing shall be made to the Assistant Administrator or administrative law judge, if one is appointed, and shall set forth the need for such evidence and its relevancy.