Congress is saying to the President: stop using the U.S. military in fighting against Iran unless Congress has formally approved it, either by declaring war or by passing a law specifically permitting military force against Iran. The move relies on the War Powers Resolution, a 1973 law that lets Congress push back when a President sends troops into fighting without its approval, and this measure is a concurrent resolution, a type of vote passed by both the House and Senate that does not go to the President for a signature. Troops needed to defend the United States, an ally, or a partner from an attack that is about to happen are not covered, as long as the President follows a rule in that same 1973 law, which generally requires bringing forces out of fighting within 60 days after Congress is told (or should have been told) about it, unless Congress approves the use of force. The people most directly affected are U.S. service members involved in any hostilities with Iran, and the President, whose ability to keep them there would be limited to those defensive situations unless Congress gives explicit approval.