Cal. Government Code § 19996.24

(a) Permanent employees who voluntarily reduce their worktime shall, upon request, be given first priority for returning to a full-time work schedule to the extent that such full-time work is available. Such permanent employees shall return to full-time employment at the request of the appointing authority pursuant to regulations adopted by the department which shall define the conditions under which such a request by the appointing authority is appropriate and provide a reasonable grace period for allowing an employee to make the necessary personal arrangements for returning to full-time employment. (b) If a layoff becomes unavoidable, persons employed on a reduced worktime basis shall not routinely be subject to the layoff ahead of full-time employees. These employees shall be subject to the same seniority and other similar considerations as full-time employees in determining the order of layoffs.