California Code, Government Code - GOV § 31631

(a) Notwithstanding any other law, a board of supervisors or the governing body of a district may, by resolution, ordinance, contract, or contract amendment under this chapter, without a change in benefits, require that members pay all or part of the contributions of a member or employer, or both, for any retirement benefits provided under this chapter. All of those payments are hereby designated as employee contributions. For members who are represented in a bargaining unit, the payment requirement shall be approved in a memorandum of understanding executed by the board of supervisors or the governing body of a district and the employee collective bargaining representative. The contributions shall be uniform either (1) with respect to all members of a recognized bargaining unit or (2) all members within each of the following categories: nonsafety subject to Section 7522.20 or safety subject to Section 7522.25.

(b) Nothing in this section shall modify a board of supervisors' or the governing body of a district's authority under law as it existed on December 31, 2012, including any restrictions on that authority, to change the amount of member contributions.