In Foster v. Kansas, Ex Rel. Johnston, Attorney-General, the United States Supreme Court considered the constitutionality of a Kansas statute that prohibited the sale of intoxicating liquors. The plaintiff, Foster, was a liquor dealer who was convicted of violating the statute. He argued that the statute violated the Fourteenth Amendment of the United States Constitution, which prohibits states from denying any person the equal protection of the laws. The Supreme Court held that the statute did not violate the Fourteenth Amendment. The Court reasoned that the state had a legitimate interest in protecting the public health and safety, and that the statute was a reasonable means of achieving that goal. The Court also noted that the statute did not discriminate against any particular class of persons, and that it applied equally to all persons. The Court concluded that the statute was a valid exercise of the state's police power, and that it did not violate the Fourteenth Amendment. The Court therefore affirmed the conviction of Foster.

In the case of Foster v. Kansas, Ex Rel. Johnston, Attorney-General, the Supreme Court was asked to decide whether a state could tax an out-of-state corporation for income earned in that state when it had no physical presence there. The majority opinion held that such taxation was unconstitutional because it violated due process under the Fourteenth Amendment and interfered with interstate commerce by discriminating against out-of-state corporations. Justice Field dissented from this decision on two grounds: firstly, he argued that Congress has exclusive authority over interstate commerce and thus any interference with such commerce must be addressed through Congressional legislation rather than judicial action; secondly, he argued that states have a right to impose taxes upon persons or property within their borders regardless of where they are incorporated or reside as long as those taxes do not interfere with federal laws or regulations governing interstate commerce. He concluded his dissent by noting that while he agreed with much of what the majority said about due process and discrimination between states regarding taxation matters, these issues should ultimately be left up to Congress instead of being decided by courts alone.