Cal. Government Code § 1157.4

(a) Employees of a county employing more than 20,000 persons, other than a city and county, 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 county, other than a city and county, or (b) whose members are comprised exclusively of the employees of such county, other than a city and county, 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 county, other than a city and county, or agencies as provided in (a) or (b) above, together with former employees of such county, other than a city and county, or agencies if such former employees (1) were employees of such county, other than a city and county, or other agencies at the time of joining such association, and (2) were members of such association at the time of ceasing to be such employees. In addition to the other requirements of this section, any employee organization for which dues are to be deducted from pay warrants shall have in membership at least 1 percent of the employees of such county, other than a city and county, provided that an employee organization which is formally recognized as the majority representative of employees of such county, other than a city and county, in an established employee representational unit shall qualify as an employee organization for which dues are to be deducted from pay warrants. (b) Notwithstanding subdivision (a), an employee organization which has in membership at least 1 percent of the total number of employees of such county, other than a city and county, on April 30, 1973, and which, on April 30, 1973, was an employee organization for which dues could be deducted from pay warrants, shall not lose such qualification for the reason that such employee organization does not have after April 30, 1973, a membership of at least 1 percent of the total number of employees of such county, other than a city and county. (c) No employee may have deductions for more than a total of two organizations under this section and under Section 1157.5.