The Secretary may make such investigations as are deemed necessary to carry out the Secretary’s responsibilities under this chapter or to determine whether a producer, importer, wholesaler, retailer, or other seller of flowers and plants, or any other person has engaged or is about to engage in any acts or practices which constitute or will constitute a violation of any provisions of this chapter, or of any order, or rule or regulation issued under this chapter. For the purpose of such investigation, the Secretary is empowered to administer oaths and affirmations, subpena witnesses, compel their attendance, take evidence, and require the production of any books, papers, and documents which 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 case of contumacy by, or refusal to obey a subpena to, any person, including a producer of flowers and plants, 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 such 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 such court as a contempt thereof. All processes in any such cases may be served in the judicial district wherein such person is an inhabitant or wherever such person may be found.