California Code, Government Code - GOV § 71637

(a) For purposes of this article, professional employees shall not be denied the right to be represented separately from nonprofessional employees by a professional employee organization consisting of those professional employees.  In the event of a dispute on the appropriateness of a unit of representation for professional employees, upon request of any of the parties, the dispute shall be submitted to the California State Mediation and Conciliation Service for mediation or for recommendation for resolving the dispute.

(b) For the purpose of this section, “professional employees” means employees engaged in work requiring specialized knowledge and skills attained through completion of a recognized course of instruction, including, but not limited to, attorneys.