Butz v. City of Muscatine was a United States Supreme Court case that dealt with the issue of taxation. The case involved a dispute between the City of Muscatine and a local businessman, John Butz. The City of Muscatine had imposed a tax on Butz's business, which Butz argued was unconstitutional. The Supreme Court ultimately sided with Butz, ruling that the tax was unconstitutional. The Court held that the tax was a violation of the Fourteenth Amendment, which states that no state shall "deny to any person within its jurisdiction the equal protection of the laws." The Court reasoned that the tax was discriminatory, as it was imposed on Butz's business but not on other businesses in the city. The Court's decision in Butz v. City of Muscatine established an important precedent for taxation in the United States. The Court's ruling made it clear that taxes must be applied equally and fairly, and that any tax that is discriminatory or arbitrary is unconstitutional. This decision has been cited in numerous cases since, and has been an important part of the legal landscape in the United States.

In Butz v. City of Muscatine, the Supreme Court was asked to decide whether a city ordinance that prohibited certain types of businesses from operating within its limits was constitutional. The majority opinion held that the ordinance did not violate any federal laws and thus could be enforced by the city. However, Justice Field dissented from this decision and argued that such an ordinance violated both due process and equal protection clauses under the Fourteenth Amendment as it unfairly targeted certain businesses without providing them with adequate notice or opportunity for appeal. He further noted that while cities have broad powers to regulate their own affairs, they cannot do so in a way which violates fundamental rights guaranteed by federal law.