Tarrifs must be congressional approved first. That means the bill must be presented, debated on, voted on, then signed.

Unless Congress has already given the president that authority.

In early 2018 President Trump imposed tariffs on steel and aluminum imports under Section 232 of the Trade Expansion Act of 1962. This law states that the president can raise tariffs on imports that pose a threat to national security. Section 232 allows the President to implement these tariffs without the approval of Congress, following an investigation by the Department of Commerce. The Commerce Department has noted that threats to national security may include “fostering U.S. dependence on unreliable or unsafe imports” or “fundamentally threatening the ability of U.S. domestic industries to satisfy national security needs.”1