Cal. Business and Professions Code § 16721.5

(a) It is an unlawful trust and an unlawful restraint of trade for a person to do the following: (1) Grant or accept a letter of credit, or other document that evidences the transfer of funds or credit, or enter into a contract for the exchange of goods or services, if the letter of credit, contract, or other document contains a provision that requires a person to discriminate against, or to certify that he, she, or it has not dealt with, another person on the basis of any characteristic listed or defined in subdivision (b) or (e) of Section 51 of the Civil Code, or on the basis of a person’s lawful business associations. (2) To refuse to grant or accept a letter of credit, or other document that evidences the transfer of funds or credit, or to refuse to enter into a contract for the exchange of goods or services, on the ground that the letter, contract, or document does not contain a discriminatory provision or certification. (b) This section shall not apply to a letter of credit, contract, or other document that contains a provision pertaining to a labor dispute or an unfair labor practice if the other provisions of that letter of credit, contract, or other document otherwise do not violate this section. (c) For purposes of this section, the prohibition against discrimination on the basis of a person’s business associations does not include the requiring of association with particular employment or a particular group as a prerequisite to obtaining group rates or discounts on insurance, recreational activities, or other similar benefits. (d) For purposes of this section, “person” shall include, but not be limited to, individuals, firms, partnerships, associations, corporations, and governmental agencies.