California Code, Government Code - GOV § 3599.59

(a) Once an employee organization is recognized as the exclusive representative of an appropriate unit, it may enter into an agreement with the employer providing for organizational security in the form of a maintenance of membership deduction.

(b) The employer shall furnish the recognized employee organization with sufficient employment data to allow the organization to calculate membership fees, and shall deduct the amount specified by the recognized employee organization from the salary or wages of every employee for the membership fee. These fees shall be remitted monthly to the recognized employee organization along with an adequate itemized record of the deductions, including, if required by the recognized employee organization, machine readable data.