7 U.S. Code § 6010 - Investigations and power to subpoena
(a) In general
The Secretary may make such investigations as the Secretary determines necessary—
(b) Power to subpoena
For the purpose of an investigation made under subsection (a) of this section, the Secretary is authorized to administer oaths and affirmations and to 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.
(2) Administrative hearings
For the purpose of an administrative hearing held under section 6008 or 6009 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.
(c) Aid of courts
In 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) of this section. The court may issue an order requiring such person to comply with such a subpoena.
Any failure to obey such order of the court 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.