WASHINGTON (Reuters) - U.S. lawmakers unveiled plans on Wednesday to use a decades-old law to force a Senate vote on whether to pull the country out of a foreign conflict, in this case the civil war in Yemen.

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Republican Senator Mike Lee, independent Bernie Sanders and Democrat Chris Murphy said they would make the first attempt to take advantage of a provision in the 1973 War Powers Act that allows any senator to introduce a resolution on whether to withdraw U.S. armed forces from a conflict not authorized by Congress.

Their action was the latest salvo in an ongoing battle between the U.S. Congress and the White House over control of military conflicts.

“We believe that, as Congress has not declared war or authorized military force, this conflict (in Yemen) is unconstitutional and unauthorized,” Sanders told a news conference.

Lawmakers have argued for years that Congress has ceded too much authority over the military to the White House.

Under the Constitution, Congress -- not the president -- has the authority to declare war. But divisions over how much control they should exert over the Pentagon have stymied efforts to pass new war authorizations.

Democratic and Republican presidents have said a 2001 authorization for the fight against al Qaeda and its affiliates justifies the Afghanistan war and the fight against Islamic State in Syria.

But Senate aides said that authorization did not apply in Yemen.

It was not immediately clear how the resolution would move forward without support from the Republican leadership. Spokesmen for Majority Leader Mitch McConnell did not immediately respond to a request for comment.

A Saudi-led coalition supported by the United States has been fighting the Iran-aligned Houthi movement in Yemen since 2015 to try to restore president Abd-Rabbu Mansour Hadi to power.

The war’s heavy toll on civilians has long been a sore point with the U.S. Congress, triggering threats to block assistance to the Saudi-led coalition.

U.S. forces are backing the coalition by refueling its aircraft and providing some intelligence support. U.S. officials have declined to say precisely how many U.S. forces are on the ground in Yemen, citing security concerns.

The war has killed more than 10,000 people, displaced more than 2 million and driven Yemen -- already the poorest country on the Arabian Peninsula -- to the verge of widespread famine.