The U.S. Supreme Court refused Monday to rule on a case challenging President Trump’s 25 percent tariffs on steel imports into the U.S. that was imposed last year.

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The decision, which the justices did not immediately comment on Monday, will leave in place the U.S. Court of International Trade’s ruling from March that allowed the president’s tariffs.

In March 2018, Trump imposed 25 percent tariffs on imported steel and 10 percent tariffs on imported aluminum. Argentina, Australia, Brazil and South Korea were exempted from the tariffs. Canada and Mexico were also exempted starting in May, Reuters reported. Trump cited national security as the reason to implement the tariffs under section 232 of the 1962 Trade Expansion Act.

A group of companies in the steel industry, including the American Institute for International Steel (AIIS), then filed a lawsuit last June to argue the tariffs on imported steel had violated the U.S. Constitution because section 232 was an "improper delegation of legislative authority and violates the principles of separation of powers and checks and balances established by the Constitution."

The steel importers said Trump does not have unbounded authority under the Constitution to regulate trade — and argued the job belongs to Congress.

“As of March 28, 2019, the steel tariffs collected have exceeded $4.5 billion, plus another $1.5 billion for aluminum on which there is a 10 percent tariff,” the group wrote in a petition for writ of certiorari before judgment to the Supreme Court.

“However, the $4.5 billion figure significantly understates the irreparable and ongoing harm to petitioner AIIS’s members and to countless other companies and individuals who have sustained losses from the reduction in imports of steel products and domestic price increases resulting from the order,” the brief to the Supreme Court stated.

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The legal challenge is at an early stage before a federal appeals court has weighed in. The case could return to the Supreme Court later.

The Associated Press contributed to this report.