California Code, Government Code - GOV § 31692

The adoption of an ordinance or resolution pursuant to Section 31691 shall give no vested right to any member or retired member, and the board of supervisors or the governing body of the district may amend or repeal the ordinance or resolution at any time except that as to any member who is retired at the time of such an amendment or repeal, the amendment or repeal shall not be operative until ninety (90) days after the board or governing body notifies the member in writing of the amendment or repeal.  In counties with a population of 5,000,000 or more, the adoption of an ordinance or resolution pursuant to Section 31691 shall remain in effect for any member heretofore or hereafter retired for as long as the board of supervisors or governing body provides similar types of benefits to any active member in current county service.