In carrying on the work authorized in this chapter, the Secretary, or any officer or employee designated by him for such purpose, shall have power to hold hearings, administer oaths, sign and issue subpenas, examine witnesses, and require the production of books, records, accounts, memoranda, and papers. Upon refusal by any person to appear, testify, or produce books, records, accounts, memoranda, and papers in response to a subpena, the proper United States district court shall have power to compel obedience thereto