Public Utilities Code § 101357

(a) The board shall determine and classify the officers and employees who shall be eligible to participate in the retirement system. However, any action by the board shall be subject to the terms and regulations of a retirement system or plan selected by the board pursuant to subdivision (a) of Section 101356, and, in the case of employees of the district represented by a labor organization, subject to the collective bargaining agreement between the labor organization and the district.

(b) The district and the labor organization representing the district’s employees in a bargaining unit shall be equally represented in the administration of the retirement system.