The dominant Shia alliance in Iraq's government wants to change the outline of a security pact with the United States.
American and Iraqi officials said earlier the draft pact was final and would not be changed.
The deal would allow US forces to stay in Iraq until 2011 and allow Iraq limited authority to prosecute troops.
The agreement has been the subject of negotiations for months and must be approved by Iraq's parliament, something that remains uncertain.
Parliamentary approval is expected to be more likely if the deal is rubber-stamped by Iraq's Political Council for National Security.
The council - composed of political leaders and the heads of parliamentary factions - met on Friday and is expected to meet again soon.
On Saturday, an estimated 50,000 supporters of the radical Shia cleric Moqtada Sadr marched in Baghdad to call for US troops to leave Iraq.
The draft in its current form was agreed after lengthy negotiations between Baghdad and Washington. The BBC reports the US is thought to see the deal as a "take it or leave it" package.
The current UN mandate for US-led coalition forces expires at the end of this year. About 144,000 of the 152,000 foreign troops deployed there are US military personnel.
