Arizona Republican Senator Jeff Flake introduced legislation Monday to nullify President Donald Trump’s steel and aluminum tariffs, calling on his colleagues to rally behind the bill.

“I said when these ill-conceived tariffs were announced last week that I would introduce legislation to would immediately nullify this very unfortunate exercise in protectionism before it can wreak havoc on our economy,” Flake said on the Senate floor. “If implemented, these tariffs will do just what tariffs have always done and lead to job losses and will stymie economic growth.”

Trump levied a 25 percent tariff on foreign steel and a 10 percent tariff on foreign aluminum last week, claiming the move would benefit the American steel and aluminum industries and national security as a whole.

“Today, I am defending America’s national security by placing tariffs on foreign imports of steel and aluminum," Trump said during the signing event on Thursday. The White House used Section 232 of the Trade Expansion Act to assert that steel and aluminum imports represented a threat to national security in order to impose the tariffs without the need for congressional approval.

Republicans in Congress expressed concerns with the tariffs when they were announced, arguing the White House could accidentally spark a harmful trade war. Trump responded to those concerns by offering temporary exemptions tied to the success or failure of ongoing NAFTA negotiations for Canada and Mexico.

Flake panned the exemptions on Monday night.

“What's worse, the president's attempt at ‘flexibility’ in the form of poorly defined exemptions only serves to harm the economy further by creating uncertainty,” he said. “Tariffs are bad enough on their own. Tariffs married with uncertainty are even worse.”

He urged his colleagues to support the bill, pointing to current economic conditions and a desire for growth.

“We have now a better climate for economic growth on both the regulatory side and the tax side. If we enter a trade war, we risk reversing those gains that we have made,” Flake said.

“We in Congress simply can't be complicit as this administration courts economic disaster in this fashion. I would urge my colleagues to join me in exercising our constitutional oversight and to invalidate these irresponsible tariffs.”