President Trump announced new tariffs Thursday in two separate proclamations, one for imports of steel [text] and one for aluminum [text]. Trump says the tariffs’ main purposes are national security, as well as economic growth, and that they will take effect in 15 days, and continue until the tariffs are expressly reduced, modified or terminated.

The steel proclamation stated:

This relief will help our domestic steel industry to revive idled facilities, open closed mills, preserve necessary skills by hiring new steelworkers, and maintain or increase production, which will reduce our Nation’s need to rely on foreign producers for steel and ensure that domestic producers can continue to supply all the steel necessary for critical industries and national defense.

The stated tariffs are set at 25 percent for steel imports and 10 percent for aluminum.

In both proclamations, Trump notes exemptions for Canada and Mexico based on renegotiations of the North American Free Trade Agreement (NAFTA), of which Trump has been highly critical since his campaign, including pushes to renegotiate in his first months in office, as well as threats to withdraw from it all together [JURIST report].

“Without this tariff and satisfactory outcomes in ongoing negotiations with Canada and Mexico, the industry will continue to decline, leaving the United States at risk of becoming reliant on foreign producers of steel to meet our national security needs — a situation that is fundamentally inconsistent with the safety and security of the American people,” Trump said in the steel proclamation.

The new tariffs are met with sharp criticism. More than 100 House GOP members, including Rep. Kevin Brady, the Texas chairman of the House Ways and Means Committee, signed a letter [text, pdf] in opposition Wednesday, arguing “tariffs are taxes that make U.S. businesses less competitive and U.S. consumers poorer” and urging the president to reconsider the idea of such broad tariffs to avoid unintended consequences.

Shortly after Trump announced the tariffs, his top economic advisor, Gary Cohn, announced his resignation [WaPo report].