In the case of Dean Milk Co. v. City of Madison, the U.S Supreme Court ruled that a city ordinance was unconstitutional because it placed an undue burden on interstate commerce. The city of Madison, Wisconsin had passed an ordinance prohibiting the sale of milk unless it had been pasteurized within five miles of the city's central square. This effectively barred out-of-state dairies from selling their products in Madison and favored local producers over those from other states, including Illinois-based Dean Milk Company who brought forth this lawsuit. The court held that while public health is a legitimate concern for state and local governments, they cannot use such concerns to discriminate against interstate commerce or protect local economic interests at its expense. It further stated that less discriminatory alternatives were available to ensure public health without disrupting interstate trade - like conducting inspections at out-of-state facilities or setting uniform standards for all milk regardless where it was produced.

The dissenting opinion in the Dean Milk Co. v. City of Madison case argued that the ordinance passed by Madison, which prohibited the sale of milk unless it was pasteurized within a five-mile radius of the city's central square, did not violate the Commerce Clause as claimed by Dean Milk Company. The dissenters believed that this regulation was a legitimate exercise of police power to protect public health and safety, rather than an attempt to discriminate against interstate commerce. They contended that there is no constitutional requirement for states or municipalities to accept lower standards from other jurisdictions just because they are involved in interstate commerce; instead, local authorities should have discretion over their own sanitary regulations provided these rules do not constitute arbitrary discrimination against out-of-state businesses.