Cal. Gov. Code § 20686

For each state safety member defined in Section 20401 and whose current and prior service pensions shall be computed pursuant to Section 21373, the normal rate of contribution shall be 8 percent and shall be made only on the compensation in excess of two hundred thirty-eight dollars ($238) per month. The Legislature reserves the right to increase the rate of contribution as it may find appropriate from time to time. No adjustment shall be included in rates adopted under this section as the result of amendments hereto, changing the time at which members may retire or the benefits members shall receive, because of time during which members have contributed at different rates prior to that adoption.