20 C.F.R. § 258.4
Service of subpoenas issued under § 258.3 may be made by any individual designated by the Board. Such individual shall deliver a copy of the subpoena to the person or persons named therein, and shall at that time tender to that person or persons the fees for one day's attendance and the transportation allowance authorized by law; Provided, however, That if the witness or witnesses be summoned to appear upon motion of the person or persons designated to conduct the hearing, no fees or transportation allowance need be tendered. Fees and transportation allowances shall be in the same amount as is allowed to witnesses in the courts of the United States. The person serving the subpoena shall make certification of the manner and time of service on the original subpoena and shall file such original subpoena with the person or persons by whom it was issued.
20 C.F.R. §258.4