31 Pa. Stat. § 700j-804
When, pursuant to any statute or regulations or orders adopted thereunder, or any ordinance or reasonable trade practice, various grades of milk are specified, orders of the board fixing minimum or maximum prices may be applicable to each grade or milk component. Orders of the board fixing minimum or maximum prices may vary in different markets, and shall designate the markets to which applicable. Such orders may likewise classify milk and milk dealers or handlers in any reasonable manner which the board deems advisable, and may vary according to the classes to which they are applicable. The orders of the board with respect to the minimum prices to be paid to producers and others shall apply to the area in which the milk is produced, or to the area in which the milk so produced is manufactured, sold or distributed, as the board shall provide, and may vary in different areas according to varying uses, grades and conditions. Each such order may classify such milk by forms, classes, grade or uses, as the board may deem advisable, and may specify the minimum prices therefor. Other reasonable methods of classification may be prescribed by the board.
31 P.S. § 700j-804