Cal. Gov't Code § 22895

(a) Notwithstanding any other provision of this part, a school employer, the employees’ exclusive representative, and unrepresented employees may agree that the employer contribution for postretirement health coverage shall be subject to the following:
1. (1) Credited years of service that the employee worked with the contracting agency.
2. (2) A memorandum of understanding regarding postretirement health coverage mutually agreed upon through collective bargaining. This issue may not be subject to the impasse procedures set forth in Article 9 (commencing with Section 3548) of Chapter 10.7 of Division 4 of Title 1.
(b) No agreement reached pursuant to subdivision (a) shall be valid if it imposes separate postretirement health coverage vesting requirements on employees in the same category and doing similar job duties.
(c) This section is not applicable to any employee who retired before the effective date of the memorandum of understanding. In the event that the memorandum of understanding establishes a retroactive effective date, this section applies only prospectively and any employee who retires before the memorandum of understanding is signed may not be affected by it.
(d) No agreement reached pursuant to subdivision (a) shall be valid if it provides an employer contribution for employees with less than five years of credited service with the school employer.
(e) The contracting agency shall provide, in the manner prescribed by the board, a notification of the agreement established pursuant to this section and any additional information necessary to implement this section.