Congress would be telling the President to pull U.S. military forces back from any active combat involvement with Iran, unless Congress has formally voted to declare war or specifically authorize that military action. There's an exception: troops can still act if they're genuinely needed to defend the U.S. or an allied country from an attack that's about to happen, but even then, the President has to follow a rule requiring Congress to be notified and give approval within 60 days if the fighting continues. In practice, this is about which branch of government — Congress or the President — gets to decide whether American troops stay engaged in conflict with Iran.