California Code, Corporations Code - CORP § 13402

(a) This part shall not apply to any corporation now in existence or hereafter organized which may lawfully render professional services other than pursuant to this part, nor shall anything herein contained alter or affect any right or privilege, whether under any existing or future provision of the Business and Professions Code or otherwise, in terms permitting or not prohibiting performance of professional services through the use of any form of corporation permitted by the General Corporation Law.

(b) The conduct of a business in this state by a corporation pursuant to a license or registration issued under any state law, except laws relating to taxation, shall not be considered to be the conduct of a business as a professional corporation if the business is conducted by, and the license or registration is issued to, a corporation which is not a professional corporation within the meaning of this part, whether or not a professional corporation could conduct the same business, or portions of the same business, as a professional corporation.