Democrats in the US are planning a challenge to President George W Bush's handling of the war in Iraq.
Some senators want to restrict the role of US troops in Iraq
Key senators are drafting legislation that would revoke the broad authority granted to the president in 2002 and replace it with a narrower mandate.
The text has not been finalised, but it is expected to restrict the role of US troops and start bringing them home.
It will face opposition from Republican senators, who have twice blocked a resolution criticising policy in Iraq.
Democratic aides have said the proposal could restrict US troops in Iraq to fighting al-Qaeda, training Iraqi forces and protecting Iraq's borders.
The Democrats argue the old authority is no longer relevant as weapons of mass destruction have not been found in Iraq, and Saddam Hussein is dead.
"We have to replace it with something because we still have troops in Iraq," Reuters news agency quotes an unnamed Democrat as saying.
"It is crazy for the president to carry on like this when the authority for the situation no longer exists."
The draft proposal is expected to be put to all Democratic senators next week.
If they approve it, the proposal could be put to the Senate, where Democrats have a slim majority and would have a struggle to see it passed.
Last Friday, the House - where the Democrats also enjoy a majority - passed a non-binding resolution against Mr Bush's plans to send an extra 21,500 troops to Iraq.
But the following day, a similar vote was blocked for the second time in the Senate.
Democrats needed the support of 60 of the 100 senators to advance the motion, but they only managed to gain 56 votes in favour.
The White House is also facing battles with Congress over funding for its $93bn (£48bn) emergency troop-funding measure.
The White House has dismissed the vote, and warned Congress against trying to cut off funding.