Gov. Code, § 20996

An employee of a contracting agency who is or was absent on military service on the effective date of the contract and who would become or would have become a member if he or she were not absent becomes or became a member on that effective date, with the same status and rights of membership as if he or she were not or had not been absent on that effective date. The employee and any other employee of a contracting agency who was absent on military service prior to that effective date shall receive credit as prior service for time during which he or she was absent on military service prior to that effective date provided that employee is entitled to receive prior service credit pursuant to Section 20933, 20934, or 20972 and he or she returned to employment of the contracting agency within six months of the termination of his or her active service with the uniformed services under conditions other than dishonorable or within six months after any period of rehabilitation afforded by the United States government other than a period of rehabilitation for purely educational purposes.

This section shall not apply to any contracting agency nor to the employees of a contracting agency until the agency elects to be subject to this section by amendment to its contract made in the manner prescribed for the approval of contracts or in the case of contracts made after January 1, 1989, by express provision in the contract making the contracting agency subject to this section.