39 C.F.R. § 913.1 – Subpoena authority.

(a) General. The General Counsel by delegation from the Postmaster General is responsible for the issuance of subpoenas in investigations conducted under 39 U.S.C. 3005(a), with authority to delegate that function to a Deputy General Counsel.
(b) Production of records. A subpoena issued by the General Counsel may require the production of any records (including computer records, books, papers, documents, and other tangible things which constitute or contain evidence) which the General Counsel considers relevant or material to an investigation.
(c) Requirements. No subpoena shall be issued until a specific case (identifying the individual or entity that is the subject) has been opened and an appropriate supervisory and legal review of a subpoena request have been performed.
(d) Requests for subpoenas.
1. (1) A request for a subpoena shall be submitted to the Office of the General Counsel by a Postal Inspector, Inspector Attorney, or other Inspector specifically authorized by the Postal Inspection Service to submit such a request, after appropriate review by an Inspector In Charge or that person's designee.
2. (2) A request for a subpoena shall state the specific case, with an individual or entity identified as the subject, in which the subpoena is requested.
3. (3) A request for a subpoena shall contain a specific description of the records requested, and shall state how they are relevant or material to the investigation.
4. (4) The General Counsel, in his or her discretion, may issue or deny the requested subpoena, or require the requesting individual to provide additional information. The General Counsel, in his or her discretion, may also honor requests to amend or supplement a request for a subpoena.
(e) Form and issuance. Every subpoena shall cite 39 U.S.C. 3016 as the authority under which it is issued, and shall command each person to whom it is directed to produce specified records at a time and place therein specified. The General Counsel shall sign the subpoena and enter the name of the individual or entity to whom it is directed.