((a)) ** .—** In conducting an investigation that the Secretary of Transportation considers necessary and proper to carry out this subtitle, the Secretary may administer oaths, take evidence, and subpoena persons to testify and produce documents relevant to the matter under investigation. Persons may be required to attend or produce documents from any place in the United States at any designated place of hearing.

((b)) ** .—** Persons subpoenaed by the Secretary under subsection (a) shall be paid the same fees and mileage paid to witnesses in the courts of the United States.

((c)) ** .—** If a person disobeys a subpoena issued under subsection (a), the Secretary may seek an order enforcing the subpoena from the district court of the United States for the district in which the person resides or does business. Process may be served in the judicial district in which the person resides or is found. The court may issue an order to obey the subpoena and punish a refusal to obey as a contempt of court.