(WASHINGTON) — A group of business groups and conservative lawyers are preparing a legal challenge to President Donald Trump’s tariffs, arguing he does not have the legal authority to impose them.

Sources familiar with the effort say they are preparing to file the challenge in the coming weeks, possibly as soon as this Friday.

One prominent legal figure close to Trump told ABC News there is “a very good chance” the U.S. Supreme Court would find Trump’s tariffs unconstitutional.

The issue is this: Congress, not the president, has the power to impose taxes and regulate trade. In imposing these tariffs, President Trump cited the 1977 International Emergency Economic Powers Act (IEEPA), which gives the the president power to regulate international commerce in the event of a national emergency.

But the IEEPA — which specifically cites the power to impose sanctions and seize foreign assets — does not mention tariffs. And, even if one argues the right to impose tariffs is implied, it’s not clear what “national emergency” could justify the imposition of global tariffs.

“There is a strong argument that the tariffs imposed under the IEEPA are not legal or constitutional,” a prominent conservative lawyer close to President Trump told ABC News. “Under that particular statute, tariffs are not listed amongst the various actions a president can take in response to the declaration of a nation emergency.”

The lawyer adds: “And when you combine that with the fact that Article 1, Section 8 [of the Constitution] clearly gives Congress the power to impose duties — tariffs — I think those two things in combination raise a very, very serious legal question.”

Another conservative lawyer familiar with the expected legal challenge to Trump’s tariffs predicted the Supreme Court would rule 9-0 against the administration if it reaches the high court.

A lawsuit has already been filed against the 20% sanctions Trump imposed on China earlier this year. The White House cited the IEEPA in imposing those tariffs as well, and the president said they were in response to China’s failure to stop the flow of fentanyl into the United States.

The suit was filed in a federal court in Florida last week by The New Civil Liberties Alliance, a conservative legal, on behalf of a Florida-based paper company called Simplified.

Trump’s tariffs are the first time a president has attempted to impose global tariffs by citing the IEEPA. The steel and aluminum tariffs Trump imposed on China during his first term where narrower and done under a different congressional authorization. But that act doesn’t specifically give the president the authority to impose tariffs — and it’s not clear what the emergency is that would justify his actions under the law.

Tariffs have never previously been imposed under the emergency power Trump is using here. The tariffs he imposed in his first term (and President Joe Biden’s tariffs, too) were imposed citing different congressional authorizations.

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