CA Gov't Code Section 1157.1

Employees of a public agency, on approval of and in accordance with the provisions made by the governing body of the public agency, may authorize deductions to be made from their salaries or wages for the payment of dues in, or for any other services provided by, any bona fide association (a) whose members are comprised exclusively of the employees of such public agency, or (b) whose members are comprised exclusively of the employees of such public agency and one or more other public agencies the payrolls of which are prepared by the same finance officer, or (c) whose members are comprised exclusively of the employees of such public agency or agencies as provided in (a) or (b) above, together with former employees of such public agency or agencies if such former employees (1) were employees of such public agency or agencies at the time of joining such association, and (2) were members of such association at the time of ceasing to be such employees.