California Code, Business and Professions Code - BPC § 16607

(a) Except as provided in subdivision (b), the customer list, including the names, addresses and identity of all employer customers who have listed job orders with an employment agency within a period of 180 days prior to the separation of an employee from the agency and including the names, addresses and identity of all applicant customers of the employment agency, shall constitute a trade secret and confidential information of, and shall belong to, the employment agency.

(b) Notwithstanding the provisions of subdivision (a), no liability shall attach to, and no cause of action shall arise from, the use of a customer list of an employment agency by a former employee who enters into business as an employment agency more than one year immediately following termination of his employment.