The Secretary may make such investigations as the Secretary deems necessary to carry out effectively the Secretary’s responsibilities under this chapter or to determine whether a person has engaged or is engaging in any acts or practices that constitute a violation of any provision of this chapter, or of any plan or regulation issued under this chapter. For the purpose of an investigation, the Secretary may administer oaths and affirmations, subpoena witnesses, compel their attendance, take evidence, and require the production of any books, papers, and documents that are relevant to the inquiry. The attendance of witnesses and the production of records may be required from any place in the United States. In case of contumacy by, or refusal to obey a subpoena issued to, any person, including a handler (or an importer who is subject to the plan), 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 requiring the attendance and testimony of witnesses and the production of books, papers, and documents; and such court may issue an order requiring the person to appear before the Secretary, there to produce records, if so ordered, or to give testimony touching the matter under investigation. Any failure to obey such order of the court may be punished by the court as contempt thereof. All process in any such case may be served in the judicial district in which the person is an inhabitant or wherever the person may be found. The site of any hearing held under this subsection shall be within the judicial district in which the person is an inhabitant or in which the person’s principal place of business is located.