California Code, Government Code - GOV § 1157.12

(a) Rely on a certification from any employee organization requesting a deduction or reduction that they have and will maintain an authorization, signed by the individual from whose salary or wages the deduction or reduction is to be made. An employee organization that certifies that it has and will maintain individual employee authorizations shall not be required to provide a copy of an individual authorization to the public employer unless a dispute arises about the existence or terms of the authorization. The employee organization shall indemnify the public employer for any claims made by the employee for deductions made in reliance on that certification.

(b) Direct employee requests to cancel or change deductions for employee organizations to the employee organization, rather than to the public employer. The public employer shall rely on information provided by the employee organization regarding whether deductions for an employee organization were properly canceled or changed, and the employee organization shall indemnify the public employer for any claims made by the employee for deductions made in reliance on that information. Deductions may be revoked only pursuant to the terms of the employee's written authorization.