Cal. Food & Agr. Code § 35751
This division does not prohibit the addition of vitamins and minerals to market milk or the sale of market milk to which any vitamins and minerals have been added if such milk is labeled to show the addition of the vitamins and minerals.
A statement of the method and manner of adding vitamins and minerals shall be filed with and approved by the director, and, when offered for sale, such vitamin and mineral milk shall not be of a standard which is below the legal requirements of market milk. When added, vitamin D shall be present in such quantity that each quart of the milk contains 400 International Units thereof within limits of good manufacturing practice. When added, vitamin A shall be present in such quantity that each quart of the milk contains not less than 2,000 International Units thereof within limits of good manufacturing practice.
The requirements of this section shall apply to all fluid market milk products.
Ca. Food and Agric. Code § 35751