The Republican-majority U.S. Senate backed legislation on Tuesday to halt U.S. military action against Iran, but it was not immediately clear how it would affect the war as President Donald Trump’s administration negotiates a peace agreement with the Islamic republic.

The Senate voted 50-48 in favor of the concurrent resolution, which passed the House of Representatives early this month, reflecting growing concern even among some of Trump’s Republicans about the unpopular conflict that began on February 28.

The vote was nearly along party lines, with four Republicans joining all but one Democrat in favor. Two Republicans did not vote.

The resolution directs Trump to remove U.S. armed forces from hostilities with or against Iran, but is likely to remain merely a symbolic vote.

Under the 1973 War Powers Act, the measure does not get sent to the White House for Trump’s signature. However, the White House has insisted the legislation is not constitutional and thus not binding.

Legal experts say it remains a contested legal question likely to be settled in the courts.

“The executive branch will likely ignore it on constitutional grounds, and it’s not clear who might have standing to sue to enforce it,” said Scott Anderson, a senior fellow at the Brookings Institution and senior editor of the online legal publication Lawfare.

(Reporting by Patricia Zengerle; additional reporting by Richard Cowan; Editing by Sanjeev Miglani)