GOP Sen. Pat Toomey Patrick (Pat) Joseph ToomeyAppeals court rules NSA's bulk phone data collection illegal Dunford withdraws from consideration to chair coronavirus oversight panel GOP senators push for quick, partial reopening of economy MORE (Pa.) on Friday announced that he would back legislation to rein in President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE's trade authority, underscoring growing GOP frustration with the administration's recent policy decisions.

“Congress should assert its constitutional responsibility and lead on trade policy so Americans keep access to affordable goods and services, and the opportunity to sell our products abroad,” Toomey said in a string of tweets explaining his decision to support Sen. Mike Lee Michael (Mike) Shumway LeeMcConnell shores up GOP support for coronavirus package McConnell tries to unify GOP Davis: The Hall of Shame for GOP senators who remain silent on Donald Trump MORE's (R-Utah) bill.

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The Trump administration on Thursday announced it would place steel and aluminum tariffs on the European Union, Canada and Mexico, ending the temporary exemptions for the key trading allies despite their two months of lobbying to avoid the tariffs.

Toomey said that implementing the tariffs under the guise of national security “weakens our credibility.”

“Claiming steel bought from our allies is a ‘national security’ threat weakens our credibility. These tariffs, i.e. taxes, hurt American workers, employers, and consumers,” Toomey tweeted Friday.

Claiming steel bought from our allies is a 'national security' threat weakens our credibility. These tariffs, i.e. taxes, hurt American workers, employers, and consumers. — Senator Pat Toomey (@SenToomey) June 1, 2018

He added that Lee's legislation would "rein in" Trump's ability to impose similar tariffs.

If passed, the bill would require congressional approval for Trump’s trade actions, including tariffs.

Aside from Toomey and Lee, three GOP senators are officially backing the legislation: Sens. Jeff Flake Jeffrey (Jeff) Lane FlakeJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden Maybe they just don't like cowboys: The president is successful, some just don't like his style MORE (Ariz.), Cory Gardner Cory Scott GardnerOvernight Health Care: US coronavirus deaths hit 200,000 | Ginsburg's death puts future of ObamaCare at risk | Federal panel delays vote on initial COVID-19 vaccine distribution The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Senate GOP sees early Supreme Court vote as political booster shot MORE (Colo.) and Ben Sasse Benjamin (Ben) Eric SasseGovernment watchdog recommends creation of White House cyber director position Chamber of Commerce endorses McSally for reelection Ben Sasse is mistaken with idea for the election of senators in America MORE (Neb.).

Republican senators have publicly fretted for months that Trump's trade policies would spark retaliation from other countries.

Trump's recent moves, including exploring separate tariffs on imported autos, have poured fuel on the tensions between Trump and GOP lawmakers, who have fundamentally different approaches to trade.

Republicans have also been upfront about the fact that they are worried Trump's trade moves could roil the economy months before a midterm election, undoing what they view as a boost from last year's tax bill.

“If this devolves into a full-blown trade war, the resulting harm will undo all of the great economic progress we’ve made with deregulation and tax reform,” Toomey added Friday.

Toomey’s support could represent a major get for Lee’s legislation. The GOP senator is considered to be within the mainstream of the Senate Republican caucuses’ thinking on financial issues and he helped craft a deal that paved the way for last year's tax bill.

Asked last week about Toomey’s assertion that tariffs on imported autos were a “bad idea,” Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellPelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Senate GOP aims to confirm Trump court pick by Oct. 29: report Trump argues full Supreme Court needed to settle potential election disputes MORE (R-Ky.) noted that he normally agrees with the Pennsylvania senator on the issue.

“I tend to agree with Toomey on that. I hope we can avoid getting into any kind of tariff situation,” Senate Majority Leader Mitch McConnell (R-Ky.) told Fox News. “I think all of us are hoping that all of this back and forth discussion about trade doesn’t end up leading into the implementation of tariffs or some larger trade war.”