7 U.S. Code § 7420 - Investigations and power to subpoena
The Secretary may make such investigations as the Secretary considers necessary—
(b) Subpoenas, oaths, and affirmations
For the purpose of any investigation under subsection (a) of this section, the Secretary may administer oaths and affirmations, subpoena witnesses, compel the attendance of witnesses, take evidence, and require the production of any records or documents that are relevant to the inquiry. The attendance of witnesses and the production of records or documents may be required from any place in the United States.
(c) Aid of courts
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 the investigation or proceeding is carried on, or where the person resides or carries on business, in order to require the attendance and testimony of the person or the production of records or documents. The court may issue an order requiring the person to appear before the Secretary to produce records or documents or to give testimony regarding the matter under investigation.
Any failure to obey the order of the court may be punished by the court as a contempt of the court.