Henderson et al. v. Mayor of the City of New York et al. was a United States Supreme Court case that addressed the issue of whether a state law could be enforced in a federal court. The case involved a dispute between the Mayor of New York City and a group of citizens who had been denied access to the city's public parks. The citizens argued that the city's law, which prohibited them from entering the parks, was unconstitutional and violated their rights under the Fourteenth Amendment. The Supreme Court held that the state law could not be enforced in a federal court, as it was in conflict with the Fourteenth Amendment. The Court also held that the city's law was unconstitutional and violated the citizens' rights. The decision in this case established the principle that state laws cannot be enforced in federal courts if they conflict with the Constitution.

In Henderson et al. v. Mayor of the City of New York et al., Justice Field delivered a dissenting opinion in which he argued that the majority had erred by failing to consider whether or not the act passed by Congress was constitutional and instead focusing on its interpretation. He noted that if it were found unconstitutional, then any attempt to enforce it would be void and thus could not be enforced against those who had acted upon it in good faith prior to its being declared as such. Furthermore, he argued that even if this particular act did pass muster with regards to constitutionality, there were still other issues at play regarding how far Congress' power extended when making laws for territories outside their jurisdiction - an issue which should have been addressed before ruling on this case. Ultimately, Justice Field concluded that while his colleagues may have reached a correct decision based on their interpretation of the law, they failed to address some important underlying questions about federalism and states' rights which needed further consideration before rendering judgement in this matter.