A bill from Senator Grassley to reassert Congress’s role in imposing tariffs is slowly gaining steam in the upper chamber, with seven GOP lawmakers now signing on to the effort. Further losses in the stock market, which many experts say may not subside in the coming week, may push more Republicans to do the same. 

The moment President Trump announced his new tariff scheme last week, index futures began tumbling, and over the course of the following days, the stock market clocked some of its worst single-day losses in years.

The morning after the tariffs were unveiled and the carnage in the stock markets began in earnest, Mr. Grassley and a Democrat, Senator Cantwell, introduced the Trade Review Act of 2025, which would require Congress to vote on a resolution approving of any new tariffs imposed, or they would expire. 

“For too long, Congress has delegated its clear authority to regulate interstate and foreign commerce to the executive branch,” Mr. Grassley said in a statement. “Building on my previous efforts as Finance Committee Chairman, I’m joining Senator Cantwell to introduce the bipartisan Trade Review Act of 2025 to reassert Congress’ constitutional role and ensure Congress has a voice in trade policy.”

By Sunday morning, six additional GOP senators had signed on to the legislation as co-sponsors. Senator Murkowski, Senator Collins, and Senator McConnell are all supporting the bill after voting for a resolution last week that would have repealed all of Mr. Trump’s new tariffs on Canada. Senator Moran, Senator Tillis, and Senator Young — all of whom come from states with large agriculture sectors — are also backing the legislation. 

Mr. Moran, who has been in Congress since the late 1990s, has long been an advocate for freer trade, especially with Canada and Mexico. When Mr. Trump announced in 2017 that he would try to renegotiate the North American Free Trade Agreement, the Kansas senator insisted that the president “should be focused on expanding exports to these neighboring countries by reducing non-tariff barriers.”

He now says that it is his job to represent Kansas and its business interests, even if the president may disagree with Congress using its power in crafting the new tariff regime. 

“Every state has unique industries that are impacted differently by changes in global markets and trade policies, such as agriculture, car manufacturing and aircraft production,” Mr. Moran told Reuters in a statement. “The Constitution gives Congress the authority to make decisions regarding foreign commerce, including tariffs.”

It is unlikely that Mr. Trump would support any kind of legislation that limits his unilateral tariff authority, meaning Congress would need to pass the bill by a veto-proof majority in order to avoid his objections. In the Senate, Mr. Grassley would need 13 additional Republicans on top of the current seven co-sponsors to win the two-thirds majority necessary to overcome  a veto, assuming all Democrats voted yes. 

The White House did not immediately respond to a request for comment asking if the president plans to veto this legislation if it gets to his desk. 

Other Republicans who could realistically sign on to the bill include Senator Cruz, who has been saying for the last week that these new tariffs will harm the economy. 

“Tariffs are a tax on consumers and I’m not a fan of jacking up taxes on American consumers,” Mr. Cruz said in an interview with Fox News. Senator Paul, who also voted to repeal the Canada tariffs, has also demanded Congress assert some power in this fight, though he has not yet signed on to Mr. Grassley’s legislation. 

In the House, the only way lawmakers could force a vote on Mr. Grassley’s bill would be to sign on to a discharge petition, a mechanism that requires a majority of the House to declare their support for a piece of legislation so that it can come to the floor. 

Those Republicans who sign the petition, however, will likely be subject to the president’s public harassment and primary threats from his supporters. Ahead of the vote to cancel his new Canada tariffs, Mr. Trump went straight at the four GOP senators who were planning to vote yes on the resolution last week. 

The president declared that the four Republicans who supported the anti-tariff resolution were “playing with the lives of the American people, and right into the hands of the Radical Left Democrats and Drug Cartels.”