California Code, Education Code - EDC § 89620

(1) Eligible employees shall irrevocably elect either to join the Public Employees' Retirement System in accordance with the provisions of law applicable thereto or to participate in the optional retirement program established pursuant to this chapter. This election is irrevocable and shall be made within 60 days of the date of employment. This election shall be in writing and filed with the California State University and the Public Employees' Retirement System. Notwithstanding Section 20303 of the Government Code, eligible employees shall not be subject to membership in the Public Employees' Retirement System until either they exercise the election to not participate in the optional retirement program or the 60-day period expires, whichever occurs first, whereupon the member contributions required by Sections 20600 and 20603 of the Government Code shall commence.

(2) An election of the optional retirement program by an eligible employee shall be irrevocable and shall be accompanied by an appropriate enrollment form, where required, for the issuance of contracts or certificates under the program.