In REA v. Missouri, the United States Supreme Court was asked to decide whether a state could impose a tax on a railroad company that was incorporated in another state. The railroad company, the Railroad Extension Association (REA), argued that the tax was unconstitutional because it violated the Commerce Clause of the United States Constitution. The Commerce Clause gives Congress the power to regulate interstate commerce. The Supreme Court held that the tax was unconstitutional because it violated the Commerce Clause. The Court reasoned that the tax was discriminatory because it only applied to railroads that were incorporated in other states. The Court also noted that the tax was not necessary to protect the interests of the state, and that it would have a negative effect on interstate commerce. The Court concluded that the tax was unconstitutional because it violated the Commerce Clause. The Court held that the state could not impose a tax on a railroad company that was incorporated in another state. This decision was important because it established that states cannot impose taxes on interstate commerce that are not necessary to protect the interests of the state.

In Rea v. Missouri, the United States Supreme Court was asked to decide whether a state statute that prohibited African Americans from testifying against white persons in criminal cases violated the Fourteenth Amendment of the U.S. Constitution. The majority opinion held that such a law did not violate any constitutional rights and thus upheld it as valid under state law. Justice Field dissented, arguing that this type of legislation denied African American citizens their right to equal protection under the law by denying them access to justice on an equal footing with whites and therefore violated both due process and equal protection clauses of the Fourteenth Amendment. He argued further that since all citizens are entitled to testify in court regardless of race or color, then any attempt by states to deny certain races or colors this right should be struck down as unconstitutional because it is inherently unequal treatment based solely on race or color which violates fundamental principles of fairness enshrined in our constitution's guarantee for equality before the law for all people regardless of race or color