Cal. Public Utilities Code § 5389

(a) The commission, each commissioner, and each officer and person employed by the commission may, at any time have access to the land, buildings, or equipment of a charter-party carrier of passengers used in connection with the operation of its business and may inspect the accounts, books, papers, and documents of the carrier. Any inspection by the commission may include photocopying or the electrostatic or photostatic reproduction of documents either at the premises of the carrier or the offices of the commission, at the option of the carrier. The commission shall reimburse the carrier for any copying or reproduction expenses incurred by it at the direction of the commission. (b) Subdivision (a) also applies to access to property and inspections of the accounts, books, papers, and documents of any business which is a subsidiary or affiliate of, or a corporation which holds a controlling interest in, a charter-party carrier of passengers with respect to any transaction between the carrier and the subsidiary, affiliate, or holding corporation. (c) Subdivisions (a) and (b) also apply to any person or corporation engaged in the transportation of persons by motor vehicle for compensation, which the commission, or an officer or person employed by the commission, determines is holding itself out as a charter-party carrier of passengers.