On October 20, the US Supreme Court ruled that President Trump exceeded his authority under the International Emergency Economic Powers Act (IEEPA) when he imposed reciprocal tariffs on most trading partners. The Court's decision determined that the power to levy taxes and tariffs is constitutionally reserved for Congress, indicating that the IEEPA did not delegate such powers to the President. This ruling was notably split 6-3 along ideological lines, with three liberal justices joining conservative justices Neil Gorsuch and Amy Coney Barrett in the majority, while justices Clarence Thomas, Brett Kavanaugh, and Samuel Alito dissented.

The Court categorized the case as involving a 'major question', asserting that significant economic and political actions, particularly those with consequences amounting to potentially trillions of dollars, cannot be decided by the President alone without clear congressional delegation. The majority opinion emphasized that there had been no precedent wherein any president utilized the IEEPA to impose tariffs for over 50 years, underscoring the importance of congressional authority in such matters.

As a result of this ruling, tariffs imposed by the Trump administration on imports from Canada and Mexico at 25%, China at rates ranging from 10% to 145%, and a minimum reciprocal tariff of 10% on all trading partners have legally lost their justification. This includes tariffs that Trump had threatened to raise to 25% based on criticisms over South Korea's investment pace in the US, showcasing the broader implications of the Court’s ruling on international trade relations and presidential economic authority.