The party requesting a subpoena shall pay the
 cost of the fees and mileage of any witness
 subpoenaed 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 authority, a check for witness fees and
 mileage need not accompany the subpoena.