7 U.S. Code § 6308 - Investigations and power to subpoena
For the purpose of an investigation under subsection (a), the Secretary may administer oaths and affirmations, and issue a subpoena to require the production of any records that are relevant to the inquiry. The production of any such records may be required from any place in the United States.
For the purpose of an administrative hearing held under section 6306 or 6307 of this title, the presiding officer is authorized to administer oaths and affirmations, subpoena witnesses, compel their attendance, take evidence, and require the production of any records that are relevant to the inquiry. Such attendance of witnesses and the production of any such records may be required from any place in the United States.
In the case of contumacy by, or refusal to obey a subpoena issued to, any person, the Secretary may invoke the aid of any court of the United States within the jurisdiction of which such investigation or proceeding is carried on, or where such person resides or carries on business, in order to enforce a subpoena issued by the Secretary under subsection (b). The court may issue an order requiring such person to comply with such a subpoena.
Any failure to obey an order of the court under this section may be punished by such court as a contempt thereof.
Process in any such case may be served in the judicial district in which such person resides or conducts business or wherever such person may be found.