The ruling said Trump overstepped his emergency powers when he imposed tariffs.

The US federal court has ruled that the US President Donald Trump overstepped his constitutional authority in imposing a series of sweeping tariffs against US trading partners, siding with a coalition of 12 US states led by Oregon and New York and small US businesses that import goods from countries targeted by the levies.

In a landmark decision issued Wednesday, May 28, the US Court of International Trade found that three sets of tariff orders—referred to as the Worldwide, Retaliatory, and Trafficking Tariff Orders—exceeded the powers granted to the president under the International Emergency Economic Powers Act (IEEPA).

“The Worldwide and Retaliatory Tariff Orders exceed any authority granted to the President by IEEPA to regulate importation by means of tariffs,” the court wrote. The decision grants summary judgment in favour of the states, cancels the tariff orders, and permanently enjoins their enforcement nationwide, meaning the government is prohibited from enforcing them in the future. The court said that under the US Constitution, Congress has exclusive powers to regulate commerce with other nations, and not the president.

The court also rejected the argument that such relief should be limited to the plaintiff states, citing the US Constitution’s requirement for uniform duties across the country. Reuters reported that the Trump administration filed a notice of appeal shortly after and questioned the authority of the court.

The ruling delivers a major legal blow to the reasoning behind many of former President Trump’s trade tariffs, which targeted hundreds of billions of dollars in imports from countries including China, Canada and Mexico. It also adds fresh uncertainty for businesses and shippers, working to avail of the 90-day tariff suspension between the US and China to frontload goods into the US.