In Taylor v. Ypsilanti, the Supreme Court of the United States was asked to decide whether a city ordinance in Ypsilanti, Michigan, was constitutional. The ordinance required all persons who owned or kept a dog within the city limits to pay a tax. The plaintiff, Taylor, argued that the ordinance was unconstitutional because it violated the Fourteenth Amendment's Equal Protection Clause. The Supreme Court held that the ordinance was constitutional. The Court reasoned that the ordinance was a valid exercise of the city's police power, and that it did not violate the Equal Protection Clause because it applied equally to all persons who owned or kept a dog within the city limits. The Court also noted that the ordinance was not a tax on property, but rather a tax on the privilege of owning or keeping a dog within the city limits. The Court concluded that the ordinance was a valid exercise of the city's police power, and that it did not violate the Equal Protection Clause. The Court's decision in Taylor v. Ypsilanti established that cities may impose taxes on the privilege of owning or keeping a dog within the city limits, so long as the tax is applied equally to all persons who own or keep a dog within the city limits.

In Taylor v. Ypsilanti, the Supreme Court was asked to decide whether a tax imposed by the City of Ypsilanti on real estate owned by non-residents violated the Constitution's Contract Clause. The majority held that it did not violate this clause because there had been no contract between the city and those affected by its taxation. Justice Field dissented from this opinion, arguing that while there may have been no express contract between them, an implied one existed due to prior laws which allowed for such taxes only when they were approved in advance by two thirds of voters living within city limits. He argued that these prior laws created an expectation among property owners outside of Ypsilanti that their properties would be taxed at a rate consistent with what was approved in advance; thus creating an implied contractual obligation between them and the City of Ypsilanti which could not be broken without violating their rights under the Contract Clause.