Sen. Jeff Flake on Monday introduced legislation that would nullify the tariffs President Donald Trump imposed last week on steel and aluminum imports.

Mexico and Canada, who along with the U.S. are in the midst of renegotiating the North American Free Trade Agreement, are initially exempt from the new tariffs, a carveout Flake said would lead to uncertainty among other countries.

“If implemented these tariffs will do just what tariffs have always done. They will lead to job losses and will stymie economic growth,” the Arizona Republican, who is retiring at the end of this year, said on the Senate floor. “Tariffs are bad enough on their own. Tariffs married with uncertainty are even worse.”

It is unclear if the legislation will advance. Senate Republicans were by-and-large unified in their opposition to the new 25 percent tariff on steel imports and a 10 percent tariff on aluminum imports that Trump announced last Thursday.

Watch: Trump Signs Steel and Aluminum Tariffs

“Members of the Senate, myself included, are concerned about the scope of the proposed tariffs on steel and aluminum and their impact on American citizens and businesses,” Senate Majority Leader Mitch McConnell said in a statement after the announcement. “Questions remain about whether ultimately these tariffs will be sufficiently targeted, tailored and limited.”

House Republicans, hoping to avoid having to push legislation on the issue, had previously hoped the president would scale back his tariff proposal before finalizing it.

“We are extremely worried about the consequences of a trade war and are urging the White House to not advance with this plan,” House Speaker Paul D. Ryan spokeswoman AshLee Strong said last week. “The new tax reform law has boosted the economy and we certainly don’t want to jeopardize those gains.”