49 CFR §1503.649

1. (a)General. Unless otherwise authorized by the ALJ, the party who applies for a subpoena to compel the attendance of a witness at a deposition or hearing, or the party at whose request a witness appears at a deposition or hearing, must pay the witness fees described in this section.
2. (b)Amount. Except for an employee of the agency who appears at the direction of the agency, a witness who appears at a deposition or hearing is entitled to the same fees and mileage expenses as are paid to a witness in a court of the United States in comparable circumstances.