Cal. Pub. Util. Code § 527
Nothing in this part shall prevent the interchange of free or reduced rate transportation for passenger or express matter between common carriers, their officers, agents, employees, attorneys, physicians and surgeons, and members of their families, where such common carriers are subject in whole or in part to the jurisdiction of the commission or of the federal Surface Transportation Board or where such common carriers, though not in whole or in part subject to the jurisdiction of this commission or of the federal Surface Transportation Board are engaged in the business of transporting passengers and freight by water between the United States and foreign countries, and are permitted by federal law to interchange such free transportation with common carriers which are subject to the jurisdiction of the Public Utilities Commission or the federal Surface Transportation Board.
Ca. Pub. Util. Code § 527