(a) Subpoenas requiring the attendance of witnesses or the presentation of a document from any place in the United States at any designated place of hearing shall be issued by the administrative law judge upon request and upon a timely showing, in writing, of the general relevance and reasonable scope of the evidence sought. Any person appearing in the proceeding may apply for the issuance of a subpoena. Such application shall identify exactly the witness or document and state fully the nature of the evidence proposed to be secured.

(b) Witnesses summoned by the Secretary shall be paid the same fees and mileage as are paid witnesses in the courts of the United States. Witness fees and mileage shall be paid by the party at whose instance witnesses appear, and the Secretary before issuing a subpoena may require a deposit of an amount adequate to cover the fees and mileage involved.