In the 1894 case of Emert v. Missouri, the United States Supreme Court examined whether a state law that taxed commercial travelers for selling goods in the state violated the Commerce Clause of the U.S. Constitution. The plaintiff, Emert, was a salesman from Kansas who sold goods in Missouri and argued that this tax impeded interstate commerce. However, after reviewing previous cases and considering constitutional principles related to states' rights to regulate trade within their borders, the court upheld Missouri's right to impose such taxes on out-of-state salesmen operating within its jurisdiction. The court reasoned that these types of laws did not interfere with Congress's power over interstate commerce because they were essentially license fees rather than direct taxes on goods or services crossing state lines.

In the dissenting opinion for Emert v. Missouri, it was argued that the state law requiring a license to sell merchandise and imposing penalties on those who did not comply was unconstitutional. The justice believed this law violated the Fourteenth Amendment by depriving citizens of their property without due process of law. He contended that selling goods is an inherent right of ownership and should not be subject to licensing or taxation beyond what is necessary for revenue purposes. Furthermore, he asserted that such laws were discriminatory as they only applied to certain types of businesses while exempting others based on arbitrary distinctions made by legislators. This selective enforcement, according to him, constituted unequal protection under the law which contradicts principles enshrined in the Constitution.