House Speaker Paul Ryan (R-Wis.) urged President Trump on Thursday to reconsider his plans to impose new tariffs on steel and aluminum imports next week, joining growing GOP opposition to a policy that many fear could spark an international trade war. 

The top House Republican’s comments come after Trump said he would place tariffs of 25 percent on steel and 10 percent on aluminum imported into the U.S. in an effort to bolster American industries against foreign competition.  

“The Speaker is hoping the president will consider the unintended consequences of this idea and look at other approaches before moving forward,” Ryan spokesman Doug Andres said on Thursday. 

{mosads}Other top GOP lawmakers and administration officials have blasted the protectionist policy as a tax hike on American workers and consumers, warning of possible repercussions in international trade. 

The stock market also reacted negatively to Trump’s plan on Thursday, tumbling nearly 500 points before recovering slightly later in the day.