Democratic Rep. Barbara Lee questions US Ambassador to the UN Nikki Haley on Capitol Hill in Washington, June 27, 2017. Andrew Harnik/Associated Press

Democratic Rep. Barbara Lee said on Tuesday that Republican House Speaker Paul Ryan stripped her amendment, which would have repealed authorization for the use of military force against ISIS, from a defense-spending bill.

"Ryan stripped my 01 AUMF repeal amdt from DOD Approps in the dead of night. This is underhanded & undemocratic. The people deserve a debate!" she tweeted Tuesday night.

Lee's amendment, which received bipartisan support, would have repealed the 2001 Authorization for Use of Military Force and made Congress pass another one to continue the campaign against ISIS.

However, Ryan told RealClearPolitics in late June that adding the amendment was a "mistake."

“There’s a right way to deal with this, and an appropriations bill I don’t think is the right way to deal with this,” Ryan said. Ryan also told RealClearPolitics that he was open to debating the AUMF but probably not this year.

A senior Republican aide told CBS that Lee's amendment would have been subject to an objection on the House floor, however, as it was attached to an appropriations bill.

Republicans then replaced Lee's amendment with another from Republican Rep. Tom Cole requiring Trump to come up with a new strategy and budget to fight ISIS, Al Qaeda, and the Taliban, Defense News reported, which the jurisdiction committee chair allowed.

—Rep. Barbara Lee (@RepBarbaraLee) July 19, 2017

The 2001 AUMF was passed shortly after September 11th and gave then-President George Bush authorization to "use all necessary and appropriate force against those nations, organizations, or persons he determines planned, authorized, committed, or aided the terrorist attacks that occurred on September 11, 2001, or harbored such organizations or persons, in order to prevent any future acts of international terrorism against the United States by such nations, organizations or persons."

The Obama administration used the 2001 AUMF to justify airstrikes against ISIS and other terrorist groups, reasoning that, since ISIS was Al Qaeda's affiliate in Iraq from 2004 to 2014, it had authority to go to war with any group that has ever been allied with Al Qaeda.

But many legal experts were quick to criticize Obama's legal reasoning.

"This is a weak argument," Cornell University Law School professor Jens David Ohlin said in 2014. "Yes, ISIS once had a relationship with al-Qaeda and Osama Bin Laden, but that prior relationship no longer governs. What matters is the current relationship."

Lee was the only member of Congress to vote against the 2001 AUMF.