Cal. Government Code § 21091

(a) Contracting agencies as defined in Section 20022, some or all of whose employees are miscellaneous members included in the federal system, may amend their contracts with the board to provide an alternate level of benefits pursuant to this article. The alternate level of benefits shall be provided to all local miscellaneous members of a contracting agency whose services are also covered under the federal system who first become members of this system on and after the contract amendment effective date and shall be made available by election to eligible members also covered under the federal system who were employees of the contracting agency prior to the effective date of the employer’s contract amendment as specified in Section 21099. (b) This article shall not apply to any agency with a memorandum of understanding that precludes any changes in the retirement coverage of the employee bargaining unit subject to that agreement.