Nearly half of the House Republican Conference sent a letter to President Donald Trump Wednesday expressing “deep concern” about his plan to impose tariffs on steel and aluminum imports and outlined steps he should take to minimize negative consequences.

Led by Ways and Means Chairman Kevin Brady and Trade Subcommittee Chairman Dave Reichert, the letter reflects warnings that congressional Republicans have been communicating to Trump since he announced plans last week to impose a broadly applied 25 percent tariff on steel imports and a 10 percent tariff on aluminum imports.

“Because tariffs are taxes that make U.S. businesses less competitive and U.S. consumers poorer, any tariffs that are imposed should be designed to address specific distortions caused by unfair trade practices in a targeted way while minimizing negative consequences on American businesses and consumers,” the GOP lawmakers wrote.

The members suggested four steps Trump should take if he does decide to move forward with tariffs:

Exclude fairly traded products and products that do not pose a national security threat. Announce a robust exclusion process to allow U.S. companies to petition for duty-free access for imports that are unavailable from U.S. sources or are needed for other extenuating circumstances. Grandfather existing contracts for steel and aluminum purchases. Conduct a short-term review of the effects of the tariffs on the economy should to determine whether the approach is working.

Watch: Ryan Says There’s a ‘Smarter’ Way to Go on Tariffs