If passed, this resolution would tell the President to pull U.S. military forces out of any combat involvement with Iran unless Congress has specifically voted to declare war or authorize that military action. There's an exception if troops are needed to defend the U.S. or an allied country from an attack that's about to happen, but even then, the President generally has to bring forces home within 60 days unless Congress gives its approval to continue. In short, this is Congress asserting its role in deciding whether the country goes to war with Iran, rather than leaving that decision solely to the President.