In the case of Pacific Express Company v. Seibert in 1891, the U.S Supreme Court ruled that a state could not impose taxes on interstate commerce activities. The dispute arose when Missouri imposed a tax on express companies operating within its borders, including Pacific Express Company which also operated across state lines. The company argued this was an unconstitutional interference with interstate commerce and refused to pay the tax. When sued by George Seibert, Missouri's auditor at that time for non-payment of these taxes, they appealed all the way up to the Supreme Court. The court sided with Pacific Express Co., stating that while states had some power to regulate businesses within their boundaries for public welfare reasons (police powers), they couldn't use this as a pretext to interfere with or burden interstate commerce - something only Congress has authority over under Commerce Clause of Constitution. This ruling reinforced federal supremacy over states in matters relating to interstate trade and helped shape future interpretations of Commerce Clause.

In the dissenting opinion for Pacific Express Company v. Seibert, Justice Bradley argued that the Missouri statute in question did not violate either the Commerce Clause or Fourteenth Amendment of the Constitution. He contended that states have a right to regulate businesses within their borders and protect their citizens from potential harm caused by those businesses. The law requiring express companies to obtain licenses and pay taxes was seen as a reasonable exercise of this power, rather than an unconstitutional burden on interstate commerce. Furthermore, he disagreed with majority's interpretation of equal protection under Fourteenth Amendment; he believed it didn't require all occupations be taxed equally but allowed for different tax rates based on nature and conditions of various professions or industries.