WASHINGTON — Seven Senate Republicans are telling President Donald Trump his aluminum and steel tariffs will endanger national security, America’s alliances and the success of the new national defense strategy.

The lawmakers urged Trump to abandon plans for global tariffs in a letter led by Senate Armed Services Subcommittee on Emerging Threats and Capabilities Chairwoman Joni Ernst, R-Iowa. They are among Republican congressional leaders, including House Speaker Paul Ryan, R-Wis., and Senate Majority Leader Mitch McConnell, R-Ky., who have urged Trump to reconsider.

Imposing tariffs broadly, they said, “risks alienating key international partners that contribute to our ability to defend our nation and maintain international stability,” and could jeopardize partnerships beneficial to U.S. military and intelligence communities.

The letter comes as Trump prepares to announce tariffs on imported steel and aluminum that would offer temporary exemptions to Canada and Mexico, a shift that could soften the blow amid threats of retaliation by trading partners. Opponents of the tariffs are spending Thursday engaged in last-minute lobbying to blunt the impact.

Trump indicated the tariffs might be unnecessary on Canada and Mexico if the North American Free Trade Agreement could be renegotiated to his satisfaction. “We’re going to be quite flexible,” he told reporters.

He also said he would start with tariffs at 25 percent on steel and 10 percent on aluminum, but would have the flexibility to raise and lower those country by country as needed.

The Trump administration has argued the tariffs fulfill the president’s campaign promise and that weaning America off imported steel and aluminum in favor of domestically produced metals would bolster economic and national security. Officials have sought to downplay the impact on consumers and jobs in the U.S.

The letter writers see things differently, however.

“As outlined in both the National Security Strategy and National Defense Strategy, maintaining relationships with allies and partners is vital to international stability and the national security of the United States,” the letter reads. “In lieu of imposing broad, global aluminum and steel tariffs that could adversely impact our relationships with several key allies, we ask that the administration consider alternative approaches to address these issues.”

Senate Republican Policy Committee Chairman John Barrasso, R-Wy; Senate Homeland Security and Governmental Affairs Committee Chairman Ron Johnson, R-Wis.; Senate Health, Education, Labor, and Pensions Committee Chairman Lamar Alexander, R-Tenn.; and Sen. James Lankford, R-Okla., joined Ernst’s letter, as did Senate Armed Services Committee members Mike Rounds, R-S.D., and Dan Sullivan, R-Alaska.

Earlier this week, the Aerospace Industries Association, which represents more than 340 major aerospace and defense companies and their suppliers, came out against the tariffs, fearful of marketplace retaliation. However, Lockheed Martin CEO Marillyn Hewson said the company was still assessing the potential impact.

The Associated Press contributed to this report.