Cal. Pub. Util. Code § 425

The employees, representatives, and inspectors of the commission may, under its order or direction, inspect and examine any books, accounts, records, memoranda, documents, papers, and correspondence kept or required to be kept by any carrier or related business referred to in this article. This section shall, to the extent deemed necessary by the commission, apply to persons who have direct or indirect control over, or who are affiliated with, any transportation agency.