As the Sunni tribal chiefs file into the bullet-scarred headquarters of the US-led coalition in the centre of Fallujah, it is immediately clear what they came to talk about.
"The constitution is weak and it casts the Sunnis aside," says one. "We have to keep Iraq united from (Kurdish) Zakho to (Shiite) Basra," says another.
The Sunni complaints from Fallujah, the former insurgent bastion, are familiar emanating from the once-powerful minority community. But then come comments that immediately grab the attention of the attending US officials.
"We are ready to participate in the referendum on the constitution - this time, even if there is intimidation, we will still vote," said Sheikh Majed Jassim al-Showah, head of the Jumela tribe.
The Sunnis, who largely boycotted January national elections in Iraq, are upset with provisions in the draft charter on federalism and the powers of the president that were finalised on Sunday.
Due to weak representation in parliament, the power of the Sunnis to impact the process has been limited. But now they have the chance to defeat the charter at a scheduled mid-October referendum.
While such an outcome would be a severe blow to the United States, the opposition to the charter appears ironically to have its side-effect on one of the US-led coalition's key goals - increasing Sunni political engagement.
According to Sheikh Majed and other tribal chiefs at the meeting, Fallujah's Sunnis are turning out in force to register themselves on the voting rosters.
"Everybody is registering to vote in the referendum - this constitution is against Iraq as a united Arab Islamic nation," Sheikh Majed said, as another tribal counterpart told how Fallujah's "imams are encouraging everybody to vote at prayers every Friday".
In the "city of the mosques", a symbol of Sunni Arab resistance against coalition forces before a massive US-led military assault to flush out insurgents in November 2004, voter participation encouraged by community leaders like imams and tribal chiefs marks a massive shift.
US officials say hundreds have been coming to sign up each day since voter registration centres opened two weeks ago in Fallujah - a claim backed up by residents.
"We're very worried about our future situation - all the Sunnis are going to vote because last time we lost our power in Iraq," said Ahmed al-Ali, a 44-year-old doctor who did not vote in national elections but has already registered his name for the referendum.
Ali said the charter writers were agents of neighbouring countries, in particular Iran, and that Sunnis were registering their names despite posters going up in the town threatening participants with death.
Fallujah, 50 kilometers (30 miles) west of Baghdad, used to be a stronghold for insurgent leaders such as Al-Qaeda frontman in Iraq Abu Musab al-Zarqawi, who has condemned any Iraqi participation in a US-sponsored political process and warned Sunni clerics two months ago not to encourage voting.
Ali said Fallujah's residents were convinced the mainly Shiite Iraqi soldiers stationed in the town were responsible for the messages, but that Zarqawi's stock had also fallen: "we know he wants to destroy Iraqi Sunnis because he told us not to vote last time."
Whether Fallujah's attitude is indicative of other towns in the restive Sunni heartland remains to be seen. US forces have effectively sealed off entry points to the city, allowing in families returning to their devastated homes, but weeding out potential insurgents.
But John Weston, a US embassy official based in Fallujah for the last 14 months, said although it was hard to predict Sunni political dynamics, Fallujah's shift in opinion was significant.
"Just six months ago people here couldn't care less about what happened in Baghdad," said Weston, who holds weekly meetings with various sectors of Fallujah society.
Local issues such as release of detainees and infrastructure improvement had traditionally dominated the agenda, Weston said, but things changed when the imams announced an oral fatwa on July 15 urging Sunnis to register.
"People are listening to their community leaders ... there will be a group that doesn't vote because of fear, but the majority does not want to repeat the mistakes of the past," Weston said.
Fallujah-based US officials - who expected Sunni negotiators in Baghdad to strike some kind of constitution deal with the Kurds and Shiites - are pleased at signs of increasing Sunni political engagement, but uneasy over the possible scenario outlined by the sheikhs.
Sunnis need a two-thirds majority in at least three provinces to defeat the charter at the October referendum. While they form a clear majority in Fallujah's Anbar province as well as Salaheddin, doubts are growing whether they can actually muster enough "No" votes in a third province, possibly Diyala, Ninevah or Tamim.
A situation where Sunnis start to engage by participating in the referendum, yet retreat back into the insurgency after losing out to their powerful Kurdish and Shiite rivals in October could be the worst-case scenario for the US-led process.
"If we vote no and the constitution passes, it's IEDs (roadside bombs) everywhere forever in Iraq," one sheikh warned the US officials.
"You cant succeed with your plans if you dont take care of us."