California Code, Government Code - GOV § 20324

(a) An employee of the Senate or the Assembly, or the respective committees thereof, whose salaries or wages are paid from the Senate Operating Fund or the Assembly Operating Fund or the Operating Funds of the Assembly and Senate, shall be deemed a “legislative employee.” A legislative employee is excluded from membership in this system unless the person files with the board an election in writing to become a member.  The election effective date shall be the start date of the current position, provided the election is received by this system within 90 days of the applicable start date.  If the election is not received by this system within 90 days from the start date, the effective date shall be the first day of the month in which the election is received by this system.  The election shall not be required of a legislative employee who was a member of this system on October 1, 1963.

(b) Upon electing to become a member, a legislative employee may further elect at any time prior to retirement to receive service credit for their prior, excluded legislative service and the legislative employee shall have the option as to how much of that prior legislative service is to be credited.  The legislative employee shall make contributions to this system as specified in Sections 21050 and 21051 for the previous service as a legislative employee for which they desire to receive service credit.