39 CFR 962.14: (Rule 14) Enforcement of subpoenas.

In the case of contumacy or refusal to obey a subpoena issued under §§ 962.9(b)(5) and 962.13 (Rules 9 and 13), the United States district courts have jurisdiction to issue an appropriate order enforcing a subpoena. Any failure to obey a district court may be punishable as contempt. If the Postal Service seeks to enforce a subpoena under this section, the Postal Service will request the Attorney General to petition the district court for the district in which a hearing under this part is being conducted or in which the person receiving the subpoena resides or conducts business to issue such an order.