CA Gov't Code Section 3581.1

Supervisory employees shall 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 supervisory employee-employer relations as set forth in Section 3581.3. Supervisory employees also shall have the right to refuse to join or participate in the activities of employee organizations and shall have the right to represent themselves individually in their employment relations with the employer.