California Code, Public Utilities Code - PUC § 494

(a) No common carrier shall charge, demand, collect, or receive a different compensation for the transportation of persons or property, or for any service in connection therewith, than the applicable rates, fares, and charges specified in its schedules filed and in effect at the time, nor shall any such carrier refund or remit in any manner or by any device any portion of the rates, fares, or charges so specified, except upon order of the commission as provided in this part, nor extend to any corporation or person any privilege or facility in the transportation of passengers or property except such as are regularly and uniformly extended to all corporations and persons.

(b) Subdivision (a) is not applicable to network railroad transportation.