Cal. Food & Agric. Code § 61382

Discrimination in price between distributors or between wholesale customers, or between consumers, that purchase milk, cream, or any dairy product of like grade and quality under like conditions of service if the effect of that discrimination may be substantially to lessen competition or to injure or destroy or prevent competition with the person that either grants or knowingly receives the benefit of the discrimination is an unlawful practice. This section does not, however, prevent differentials which make only due allowance for differences in the cost of the raw product which is used in the milk, cream, or dairy product, or the cost of manufacture, processing, sale, or delivery which results from the different methods or quantities in which the commodities are manufactured, processed, sold, or delivered.