California Code, Health and Safety Code - HSC § 40717.9

(a) Notwithstanding Section 40454, 40457, 40717, 40717.1, or 40717.5, or any other provision of law, a district, congestion management agency, as defined in subdivision (b) of Section 65088.1 of the Government Code, or any other public agency shall not require an employer to implement an employee trip reduction program unless the program is expressly required by federal law and the elimination of the program will result in the imposition of federal sanctions, including, but not limited to, the loss of federal funds for transportation purposes.

(b) Nothing in this section shall preclude a public agency from regulating indirect sources in any manner that is not specifically prohibited by this section, where otherwise authorized by law.