The U.S. Senate passed a resolution Wednesday to end American support for the Saudi-led coalition involved in the Yemen war against Iran-backed Houthi rebels.
The resolution was passed with a 54-46 vote that saw seven Republican senators shoring up the measure.
Once it becomes a law, the proposal would give President Donald Trump 30 days, after endorsement, to end all military assistance.
The measure will now head to the Democrat-led House of Representatives, which is expected to pass it. It will then be put on Trump's desk.
The White House has already threatened to veto the legislation, which it says is flawed and could undermine the fight against extremism.
"The joint resolution would raise serious constitutional concerns to the extent that it seeks to override the President's determination as Commander in Chief," the White House said.
"The United States, with little media attention, has been Saudi Arabia's partner in this horrific war," Senator Bernie Sanders, the lead author of the measure, said.
"We have been providing the bombs the Saudi-led coalition is using. We have been refueling their planes before they drop those bombs. And we have been assisting with intelligence," Sanders said. "In too many cases, our weapons are being used to kill civilians."
Republican Senator Mike Lee, who also sponsored the bill, called the war "unconstitutional, unjustified and ultimately immoral."
"Congress must be involved in deciding if and when to put American blood and treasure on the line," he stressed.
If it passes in the House and becomes a law, it would be the first time in history Congress has invoked the 1973 War Powers Resolution, which says Congress determines when the U.S. goes to war, not the president.
“Today, we begin the process of reclaiming our constitutional power by ending U.S. involvement in a war that has not been authorized by Congress and is clearly unconstitutional,” Senator Bernie Sanders said.