The United States, Plaintiffs in Error, v. John J. Walker and Arthur F Hopkins was a case heard by the US Supreme Court in 1859. The plaintiffs argued that they had been wrongfully charged with violating an act of Congress which prohibited the importation of slaves into any port or place within the jurisdiction of the United States from any foreign kingdom, place or country. They claimed that their actions were not illegal because they did not know about this law when importing slaves to New Orleans from Cuba and thus could not be held liable for breaking it. The court ultimately ruled against them on grounds that ignorance of a law is no excuse for its violation and upheld their conviction under the act prohibiting slave importation into US ports or places from foreign countries.

In the United States Supreme Court case of The United States v. John J. Walker and Arthur F Hopkins, the dissenting opinion was that there is no constitutional authority for Congress to pass a law which would allow them to take possession of property without due process or just compensation. This opinion argued that if such a power were allowed, it could be used by Congress in an arbitrary manner and lead to unconstitutional takings of private property without any legal recourse available for those affected. Furthermore, this dissent argued that allowing such powers would undermine the fundamental principles of justice enshrined in both state and federal constitutions as well as violate natural rights protected under common law doctrines like "eminent domain". Ultimately, this dissent concluded that while Congress may have certain implied powers not explicitly stated in the Constitution, they do not extend so far as taking away citizens' right to their own property without proper legal proceedings being followed first.