The Supreme Court on Monday refused to hear a challenge to President Trump’s $4.5 billion in tariffs on steel products.

The claim was brought by the American Institute for International Steel, which argued Section 232 of the Trade Expansion Act, which Trump used to impose the duties on national security grounds, unconstitutionally delegated legislative power to the president.

Its lawsuit was previously rejected by a three-judge panel of the Court of International Trade, which sided with the Trump administration.

Trump tacked a 25% tariff onto all imported steel products more than a year ago, in March 2018. The appellants said the provision he used, part of a 1960s law, effectively empowers the president "to make the kinds of distributional and policy choices that the Constitution assigns to Congress."