Vice President Tariq al-Hashemi vetoed the legislation earlier this week. He wants more votes allocated for Iraqis living abroad, most of whom are Sunnis like him.
Lawmakers plan to vote Saturday on whether to send the same law back to the presidency council
- where it is likely to be vetoed again - or to amend the bill to address al-Hashemi's concerns.
Parliament can override a second veto with a three-fifths majority.
The U.S. has tied the pace of its troop withdrawal to the vote, but says the schedule is on track for now.