In 1977, Minnesota passed a statute banning the retail sale of milk in plastic, nonreturnable, nonrefillable containers, but permitted sales in other nonreturnable, nonrefillable containers, such as paperboard milk cartons. The legislature argued that the statute was passed to address solid waste and other environmental concerns in the state. Clover Leaf Creamery Co. and other Minnesota and non-Minnesota plastic producers and dairies (plaintiffs) brought suit against the State of Minnesota (defendant) in district court seeking to enjoin enforcement of the statute. Clover Leaf alleged that the actual purpose of the Minnesota legislature was to promote the interests of certain segments of the local dairy and pulpwood industries at the expense of the economic interests of other segments of the dairy industry and plastics industry. The district court agreed with this argument and struck down the statute, and the state supreme court affirmed after an extensive hearing. The United States Supreme Court granted certiorari.