Cal. Business and Professions Code § 21200

It is unlawful for any refiner, distributor, manufacturer, or transporter of motor vehicle fuels or oils engaged in business in this state, either directly or indirectly, to discriminate in price between different purchasers of motor vehicle fuels or oils of like grade and quality, where the effect of such discrimination is to lessen competition, or to injure, destroy, or prevent competition with any person who either grants or knowingly receives the benefit of such discrimination, or with customers of either of them. Upon proof being made, at any hearing on a complaint under this section, that there has been such discrimination in price, the burden of rebutting the prima facie case thus made by showing justification shall be upon the person charged with a violation of this section. Nothing herein contained shall prevent a seller rebutting the prima facie case thus made by showing that his lower price to any purchaser or purchasers was made in good faith to meet an equally low price of a competitor and was also offered to any other of his purchasers in competition with the purchaser or purchasers receiving such lower price. If such lower price should be incorporated into a term contract, no such contract shall as to such discriminatory price be valid for more than one year. Nothing in this section shall prevent differentials which make only due allowance for differences in the cost of manufacture, marketing, transportation, sale, or delivery resulting from the differing methods or quantities in which such commodities are to such purchasers sold or delivered. Nothing in this section shall prevent persons engaged in selling motor vehicle fuels or oils in this state from selecting their own customers in bona fide transactions and not in restraint of trade. Nothing in this section shall prevent price changes from time to time where in response to changing conditions affecting the market for, or the marketability of, the products concerned, such as, but not limited to, actual or imminent deterioration of products, distress sales under court process, or sales in good faith in discontinuance of business in the products concerned. Nothing in this section shall apply to the purchase of motor vehicle fuels or oils for their own use by state and local agencies or public utilities.