Issuance of subpenas. The attendance of witnesses and the production of documentary evidence from any place in the United States on behalf of any party to the proceeding may, by subpena, be required at any designated place of hearing. Subpenas may be issued by the Secretary or by the judge, under the facsimile signature of the Secretary, upon a reasonable showing by the applicant of the grounds, necessity, and reasonable scope thereof.

Application for subpena duces tecum. Subpenas for the production of documentary evidence, unless issued by the judge upon his own motion, shall be issued only upon a certified written application. Such application shall specify, as exactly as possible, the documents desired and shall show their competency, relevancy, and materiality and the necessity for their production.

Service of subpenas. Subpenas may be served (1) by a United States Marshal or his deputy, or (2) by any other person who is not less than 18 years of age, or (3) by registering and mailing a copy of the subpena addressed to the person to be served at his or its last known residence or principal place of business or residence. Proof of service may be made by the return of service on the subpena by the United States Marshal or his deputy; or, if served by an individual other than a United States Marshal or his deputy, by an affidavit of such person stating that he personally served a copy of the subpena upon the person named therein; or, if service was by registered mail, by an affidavit made by the person mailing the subpena that it was mailed as provided in this paragraph and by the signed return post office receipt: Provided, That, if the subpena is issued on behalf of the Department, the return receipt without an affidavit of mailing shall be sufficient proof of service. In making personal service, the person making service shall leave a copy of the subpena with the person subpenaed; the original, bearing or accompanied by the required proof of service, shall be returned to the official who issued the same.