If Congress hasn't formally voted to declare war or approve military action against Iran, this resolution would require the President to pull U.S. troops out of any combat involving Iran. It's essentially Congress asserting its constitutional authority over war decisions, rather than letting the President start or continue military action against Iran on his own. There's an exception, though: U.S. forces could still act in self-defense if the U.S. or its troops or facilities elsewhere are attacked.