(CNN) Republican Sen. Mike Lee of Utah has agreed to co-sponsor Sen. Bernie Sanders' legislation that would freeze funding for any military action in Iran without express approval from Congress.

Sanders, a Vermont independent who's running for the Democratic presidential nomination, introduced the bill shortly after the Trump administration held a classified briefing in which advisers outlined the case for their military strike last week that killed Iranian Gen. Qasem Soleimani.

Sanders was sharply critical of the briefing, saying afterward that the administration's briefers gave no proof of any imminent attack by Iran against US targets.

"They are justifying the assassination of Qasem Soleimani by claiming that he was planning 'imminent attacks' on hundreds of Americans in the region and yet they produced no evidence that would justify this claim, not even in a classified setting," Sanders said in a statement.

Lee becomes the first Republican in the Senate to sign on to the bill. During his time in the Senate, Lee has been consistently opposed to American intervention in foreign conflicts and was also highly critical of the administration's briefing on Iran. He called it "insulting and demeaning" and added that it was "the worst briefing I've seen, at least on a military issue."

Sanders and Lee have teamed up before to push legislation asserting congressional oversight of military issues. They spearheaded a bipartisan war powers resolution to end US support for the military conflict in Yemen. The bill passed both the House and Senate but was vetoed by President Donald Trump.

In a joint statement to CNN, the two senators said that while they don't agree about much, this is an issue where they have common ground.

"As United States Senators, we often disagree on many issues. But standing up for the Constitution is not about partisanship. The Founding Fathers were absolutely clear. They wanted to ensure that our country avoided needless conflict and they understood that presidential war-making would be harmful to our democracy," they said in the statement.

The House has already passed a war powers resolution aimed at keeping the administration from striking Iran without congressional approval. Three Republicans joined Democrats in passing that bill, which now goes to the Senate. A bill similar to the one being introduced by Sanders that would utilize the power of the purse to limit the military intervention is also being introduced.

Sanders already has 11 Democratic co-sponsors for the "No War with Iran Act," including Senate Minority Leader Chuck Schumer of New York.