In carrying on the work herein authorized, the Secretary of Agriculture, 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, take depositions, and require the production of books, records, accounts, memoranda, and papers, and have access to office and warehouse premises. Upon refusal by any person to appear, testify, or produce pertinent books, records, accounts, memoranda, and papers in response to a subpena, or to permit access to premises, the proper United States district court shall have power to compel obedience thereto.