United States v. Barnett was a United States Supreme Court case that addressed the issue of whether a federal statute that prohibited the sale of adulterated or misbranded food was constitutional. The defendant, Barnett, was charged with selling adulterated and misbranded food in violation of the federal statute. Barnett argued that the statute was unconstitutional because it was an unconstitutional exercise of Congress’s power to regulate interstate commerce. The Supreme Court held that the statute was constitutional. The Court reasoned that Congress had the power to regulate interstate commerce, and that the statute was a valid exercise of that power. The Court noted that the statute was necessary to protect the public health and safety, and that it was a reasonable means of doing so. The Court also noted that the statute was not overly broad or vague, and that it did not interfere with the states’ ability to regulate food safety. In conclusion, the Supreme Court held that the federal statute prohibiting the sale of adulterated or misbranded food was constitutional. The Court reasoned that the statute was a valid exercise of Congress’s power to regulate interstate commerce, and that it was necessary to protect the public health and safety. The Court also noted that the statute was not overly broad or vague, and that it did not interfere with the states’ ability to regulate food safety.

Justice Harlan delivered the dissenting opinion in United States v. Barnett, arguing that the majority's decision was inconsistent with prior Supreme Court precedent and would lead to an unjust result. He argued that Congress had not intended for a taxpayer to be held liable for taxes on income from property acquired before the tax law went into effect, as this would constitute a retroactive application of the law which is prohibited by both common sense and established legal principles. Furthermore, he noted that such a ruling could have far-reaching implications beyond just this case; if applied broadly it could potentially subject taxpayers to liability for taxes on all past transactions regardless of when they occurred or how long ago they took place. In conclusion, Justice Harlan asserted that while Congress may impose new taxes prospectively only, any attempt at imposing them retrospectively should be struck down as unconstitutional.