Cal. Pub. Util. Code § 797

The commission shall periodically audit all significant transactions, as specified by the commission, between an electrical, gas, or telephone corporation and every subsidiary or affiliate of, or corporation holding a controlling interest in, that electrical, gas, or telephone corporation. The commission may, in this connection, utilize the services of an independent auditor, who shall be selected and supervised by the commission. Nothing in this section prohibits the commission from auditing any transaction between an electrical, gas, or telephone corporation and any subsidiary or affiliate of, or corporation holding a controlling interest in, the electrical, gas, or telephone corporation, as otherwise permitted or required by law.