28 CFR 76.25: Fees.

Unless otherwise ordered by the Judge, the party requesting a subpoena shall pay the cost of the fees and mileage of any witness subpoenaed. Such costs shall be in the amounts that would be payable to a witness in a proceeding in United States district court. A check for witness fees and mileage shall accompany the subpoena when served, except that when a subpoena is issued on behalf of the complainant, a check for witness fees and mileage need not accompany the subpoena.