In the case of Schollenberger v. Pennsylvania, 1897, the Supreme Court ruled that a state law prohibiting the sale of oleomargarine colored to resemble butter was unconstitutional. The court held that while states have broad powers to regulate commerce within their borders for health and safety reasons, they cannot use this power in a way that discriminates against or burdens interstate commerce. In this case, Pennsylvania had passed a law making it illegal to sell oleomargarine colored like butter even though it was not harmful or misbranded. This effectively banned an entire class of goods from other states solely because local dairy farmers felt threatened by competition from cheaper margarine producers in other states. The court found such protectionist measures violated the Commerce Clause of the Constitution which gives Congress exclusive authority over interstate trade.

In the dissenting opinion for Schollenberger v. Pennsylvania, Justice Harlan argued that the state had a right to protect its citizens from harmful products and practices. He believed that it was within the state's police power to regulate commerce in order to safeguard public health and welfare. In this case, he felt that Pennsylvania was justified in banning oleomargarine due to concerns about its potential harm as well as fraudulent sales tactics used by manufacturers who passed it off as butter. Harlan disagreed with the majority's interpretation of interstate commerce regulations, arguing instead for a more flexible understanding which would allow states greater autonomy in protecting their residents' wellbeing.