Upon his own motion or on application of any person affected by any ruling of any agency of the United States in relation to any proposal or contract involving any of the provisions of sections 35 to 45 of this title, and on complaint of a breach or violation of any representation or stipulation as provided in said sections, the Secretary of Labor, or an impartial representative designated by him, shall have the power to hold hearings and to issue orders requiring the attendance and testimony of witnesses and the production of evidence under oath. Witnesses shall be paid the same fees and mileage that are paid witnesses in the courts of the United States. In case of contumacy, failure, or refusal of any person to obey such an order, any District Court of the United States or of any Territory or possession within the jurisdiction of which the inquiry is carried on, or within the jurisdiction of which said person who is guilty of contumacy, failure, or refusal is found, or resides or transacts business, upon the application by the Secretary of Labor or representative designated by him, shall have jurisdiction to issue to such person an order requiring such person to appear before him or representative designated by him, to produce evidence if, as, and when so ordered, and to give testimony relating to the matter under investigation or in question; and any failure to obey such order of the court may be punished by said court as a contempt thereof; and shall make findings of fact after notice and hearing, which findings shall be conclusive upon all agencies of the United States, and if supported by the preponderance of the evidence, shall be conclusive in any court of the United States; and the Secretary of Labor or authorized representative shall have the power, and is authorized, to make such decisions, based upon findings of fact, as are deemed to be necessary to enforce the provisions of sections 35 to 45 of this title