The party requesting a subpoena shall pay the cost of the fee and mileage of any witness subpoenaed in the amounts that would be payable to a witness in a proceeding in the 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 Broadcasting Board of Governors, a check for witness fees and mileage need not accompany the subpoena.