(a) Witnesses, whether appearing voluntarily or pursuant to a subpoena, shall be paid the fee and mileage allowances which are paid subpoenaed witnesses in the courts of the United States. However, any witness who is employed by the Federal Government shall not be entitled to receive witness fees.

(b) Witness fees, as appropriate, as well as transportation and per diem expenses for a witness shall be paid by the party that calls the witness to testify.