Gov. Code, § 20305

(a) An employee whose appointment or employment contract does not fix a term of full-time, continuous employment in excess of six months is excluded from this system unless:

(1) They are a member at the time they render that service and are not otherwise excluded pursuant to this article or by a provision of a contract.

(2) Their position requires regular, part-time service for one year or longer for at least an average of 20 hours per week, or requires service that is equivalent to at least an average of 20 hours per week for one year or longer, unless they elect membership pursuant to Section 20325.

(3) Their employment is, in the opinion of the board, on a seasonal, limited-term, on-call, emergency, intermittent, substitute, or other irregular basis, and is compensated and meets one of the following conditions:

(A) The appointment or employment contract does not fix a term of full-time, continuous employment in excess of six months, but full-time employment continues for longer than six months, in which case membership shall be effective not later than the first day of the first pay period of the seventh month of employment.

(B) The person completes 125 days, if employed on a per diem basis or, if employed on other than a per diem basis, completes 1,000 hours within the fiscal year, in which case, membership shall be effective not later than the first day of the first pay period of the month following the month in which 125 days or 1,000 hours of service were completed. For purposes of this subdivision, “day” means each eight-hour period of employment worked by an employee paid on a per diem basis so that membership is effective after they have completed 1,000 hours of compensated service in a fiscal year.

(C) The person is employed by the Department of Forestry and Fire Protection in one of the positions that provide state safety membership pursuant to Section 20400 or state peace officer/firefighter membership pursuant to Section 20392.

(4) They are a temporary faculty member of the California State University and meets one of the following conditions:

(A) They work two consecutive semesters or three consecutive quarters at half-time or more, and are not otherwise excluded pursuant to this article, in which case, membership shall be effective with the start of the next consecutive semester or quarter if the appointment requires service of half-time or more.

(B) They work two consecutive semesters or three consecutive quarters at a minimum teaching load of six weighted units, and are not otherwise excluded pursuant to this article, in which case membership shall be effective at the start of the next consecutive semester or quarter, but not earlier than July 1, 2004, if the appointment requires service of six weighted units or more. This subparagraph does not apply to faculty members unless provided for in a memorandum of understanding agreed upon, on or after January 1, 2003, pursuant to Chapter 12 (commencing with Section 3560) of Division 4 of Title 1, or authorized by the Trustees of the California State University for employees excluded from collective bargaining.

(5) They are a member of the Alcoholic Beverage Control Appeals Board, the Central Valley Flood Protection Board, the Board of Prison Terms, the State Personnel Board, or the State Air Resources Board and elect to become a member pursuant to Section 20320.

(6) They are participating in partial service retirement, pursuant to Article 1.7 (commencing with Section 19996.30) of Chapter 7 of Part 2.6.

(7) They are included by specific provision of the board relating to the exclusion of less than full-time employees.

(b) This section shall supersede any contract provision excluding persons in any temporary or seasonal employment basis and shall apply only to persons entering employment on and after January 1, 1975. Except as provided in Section 20502, no contract or contract amendment entered into after January 1, 1981, shall contain any provision excluding persons on an irregular employment basis.