Cal. Const. art. XII, § 4

The commission may fix rates and establish rules for the transportation of passengers and property by transportation companies, prohibit discrimination, and award reparation for the exaction of unreasonable, excessive, or discriminatory charges. A transportation company may not raise a rate or incidental charge except after a showing to and a decision by the commission that the increase is justified, and this decision shall not be subject to judicial review except as to whether confiscation of property will result.