Cal. Gov. Code § 3599.56

Employees have the right to form, join, and participate in the activities of employee organizations of their own choosing for the purpose of representation on all matters of employer-employee relations. Employees also have the right to refuse to join or participate in the activities of employee organizations, except that the parties are not precluded from agreeing to a maintenance of membership provision pursuant to a memorandum of understanding. In any event, employees have the right to represent themselves individually in their employment relations with the employer.