The U.S. Supreme Court dealt a major blow to President Donald Trump’s trade agenda Friday, ruling the tariffs he issued under the International Economic Emergency Powers Act are illegal.

In a 6-3 decision authored by Chief Justice John Roberts, the court said Congress alone holds the power to tax in almost all circumstances. The Trump administration’s argument that trade deficits and illegal drug imports granted it emergency power to levy tariffs was not justified, the court said. Tariffs are taxes on imported goods.

The Trump administration had argued that a provision in the law, known as IEEPA, that said the executive branch could “regulate” imports empowered the president to levy tariffs.

“Based on two words separated by 16 others (in the law)—‘regulate’ and ‘importation’—the President asserts the independent power to impose tariffs on imports from any country, of any product, at any rate, for any amount of time,” Roberts wrote. “Those words cannot bear such weight.”

Justices Sonia Sotomayor, Elena Kagan, Neil Gorsuch, Amy Coney Barrett and Ketanji Brown Jackson joined Roberts’ opinion.

Justices Clarence Thomas and Brett Kavanaugh filed dissenting opinions. Thomas and Justice Samuel Alito joined Kavanaugh’s.

Kavanaugh’s dissent accepted the administration’s reading of the law and said it was not the justices’ role to decide a policy matter that has “generated vigorous” debate.

“The sole legal question here is whether, under IEEPA, tariffs are a means to ‘regulate . . . importation,’” he wrote. “Statutory text, history, and precedent demonstrate that the answer is clearly yes: Like quotas and embargoes, tariffs are a traditional and common tool to regulate importation.”