Sunni Arabs have reacted angrily to a decision by Iraq's Shia-dominated parliament making it harder to reject the new constitution in 12 days' time.
The two-thirds majority needed in three provinces to defeat the constitution will now be counted from all registered - as opposed to actual - voters.
Many registered voters may not show up because of violence, it is argued.
Saleh al-Mutlaq, of the Sunni group Iraqi National Dialogue, called the change a "clear forgery".
"They want this constitution to pass despite the will of the people," he added.
BBC Baghdad correspondent Caroline Hawley says violence, intimidation and US military offensives could keep many Sunnis away from polling centres.
'Implausible' change
The interim constitution drawn up under US administrator Paul Bremer in 2003 says the following about the issue:
"The general referendum will be successful and the draft constitution ratified if a majority of the voters in Iraq approve and if two-thirds of the voters in three or more governorates do not reject it."
But on Sunday, MPs said a No vote from two-thirds of "registered" voters was needed for a veto.
The new interpretation keeps the clause stipulating that only half of actual voters are needed for the text to be adopted.
Many Sunni Arabs oppose the draft constitution on the grounds that its federal provisions could lead to the break-up of Iraq.
In elections for the transitional parliament in January, less than 60% of registered Iraqis voted after Sunni leaders called for a boycott.
It's a bad situation and this change will certainly inflame the opponents. But it is a change that can be argued for. If people don't vote due to intimidation, then how can the real will of the people be known? If a constitution that the vast majority of Iraqi voters want is rejected under threats in a few areas, then how is that respecting the will of the people either? In other words, why should the insurgents get to dictate whether the constitution is approved?
The best solution for constitution supporters would be for there to be a large turnout of people who vote yes in the Sunni areas. The best situation for Sunnis who are opponents is to turn out in large numbers and not boycott the vote. Maybe we'll be surprised.
I'm hopeful that some sort of constitution will be approved and that the politicians will then work together to modify it as needed to protect the rights of everyone. Yeah, I'm an optimist.
Cheers,
Scott.