66 Pa. C.S. § 506
The commission shall have full power and authority, either by or through its members, or duly authorized representatives, whenever it shall deem it necessary or proper in carrying out any of the provisions of, or its duties under this part, to enter upon the premises, buildings, machinery, system, plant, and equipment, and make any inspection, valuation, physical examination, inquiry, or investigation of any and all plant and equipment, facilities, property, and pertinent records, books, papers, accounts, maps, inventories, appraisals, valuations, memoranda, documents, or effects whatsoever, of any public utility, or prepared or kept for it by others, and to hold any hearing for such purposes. In the performance of such duties, the commission may have access to, and use any books, records, or documents in the possession of, any department, board, or commission of the Commonwealth, or any political subdivision thereof.
66 Pa.C.S. § 506