The U.S. is continuing its negotiation over the trade of steel and aluminum with Canada and Mexico, Trade Representative Robert Lighthizer told members of a legislative committee this week. 

Last March, the Trump administration said they would set tariffs of 25 percent for steel and aluminum imports from Mexico and Canada, saying at the time that it was a matter of national security.

The immediate result has been a predictable supply-demand outcome. Steel is now more expensive in the U.S., and companies that use large volumes of it have had to raise their prices on products such as cars. 

On a larger scale, the tariffs have made it difficult for those corporations to do long-term planning, said Vanessa Sciarra, vice president of the Washington D.C.-based National Foreign Trade Council.

“Businesses don’t just make decisions for next week,” Sciarra said. “They make decisions for six to nine months from now, and when you tell a business these tariffs have no end date, you basically create uncertainty.”

Both Canada and Mexico have sought to pressure the U.S. to remove the tariffs. Canada is the single largest supplier of both aluminum and steel to the United States. Mexico, on Friday, threatened to slap duties on new U.S. products in retaliation for the tariffs, Reuters reported.