President Trump’s “Liberation Day” tariffs came under their first major legal challenge Monday, brought by a libertarian public-interest firm that argues the president overstepped his authority. 

Trump’s April 2 announcement imposed a baseline 10 percent tariff on imports and targeted dozens of countries with higher “reciprocal” tariffs. 

The announcement has rattled stock and bond markets, and Trump later announced the steeper tariffs would be reduced to 10 percent for 90 days to allow time for negotiations. 

Monday’s lawsuit contests Trump’s ability to impose the tariffs unilaterally by invoking the International Emergency Economic Powers Act (IEEPA). The 1977 law provides the president with the authority to impose necessary economic sanctions to combat an “unusual and extraordinary threat,” but no previous president has leveraged it to impose tariffs. 

“Our system is not set up so that one person in the system can have the power to impose taxes across the world economy. That’s not how our constitutional republic works,” Jeffrey Schwab, senior counsel at Liberty Justice Center, which is leading the lawsuit, said in an interview. 

“And so that is the thing that we’re very concerned about. Because today it’s tariffs, but could it be something else in the future,” Schwab continued. 

The Liberty Justice Center, a libertarian public-interest firm that regularly represents conservative causes, filed the lawsuit in partnership with Ilya Somin, a law professor at George Mason University’s Antonin Scalia Law School. 

They did so on behalf of a group of five small businesses impacted by the tariffs: wine and spirits company VOS Selections, sportfishing e-commerce business FishUSA, electric toy designer MicroKits, pipe maker Genova Pipe and women’s cycling apparel brand Terry Precision Cycling. 

The suit was filed in the U.S. Court of International Trade, which has exclusive jurisdiction over certain lawsuits involving import transactions. 

Four members of the Blackfeet Nation previously sued over Trump’s Canada tariffs, including the Canadian aspects of his April 2 announcement. But Monday’s suit is far broader and challenges Trump’s “Liberation Day” tariffs across the globe.

It adds to a lawsuit filed by the New Civil Liberties Alliance earlier this month challenging some of Trump’s additional tariffs imposed on China.

“If starting the biggest trade war since the Great Depression based on a law that doesn’t even mention tariffs is not an unconstitutional usurpation of legislative power, I don’t know what is,” Somin said in a statement.

Updated 2:17 p.m.