Cal. Pub. Util. Code § 30451

The adoption, terms, and conditions of the retirement systems covering employees of the district in a bargaining unit represented by a labor organization shall be pursuant to a collective bargaining agreement between such labor organization and the district. Any such retirement system adopted pursuant to a collective bargaining agreement shall be on a sound actuarial basis. The district and the labor organization representing the district’s employees in a bargaining unit shall be equally represented in the administration of such retirement system.