By David Loyn
BBC News, Baghdad
Parliament faces a 22 October deadline on the federal issue
The live television feed from the Iraqi parliament was cut on Thursday amid rowdy scenes over federalism.
When order was restored, the Speaker agreed to a full debate on Sunday.
With little more than a month before a 22 October deadline to resolve the process of how regions can win federal autonomy, this contentious issue is threatening to derail other parliamentary business.
The battle lines are complex, but it is the Sunni Arab minority who fear that they could lose most.
They feel they may be left with a wedge of land in the middle of the country and no access to oil, while the nine provinces of the south secede under a Shia-dominated government and the north falls into the hands of a resurgent Kurdistan.
Some now openly voice nostalgia for the days of Saddam Hussein, who kept the Sunni minority in power, ruthlessly crushing opposition in the north and south.
Arguments over federalism threatened to derail the whole process of writing a new constitution after he fell.
The compromise that just kept Sunni politicians on board then was to delay discussion. But it could not be delayed for ever.
In parliament Ala Makki, a leading member of the mainly Sunni Iraqi Islamic Party, said that his party had no disagreement with the principle of federalism as long as all of Iraq remained under the "supervision of a strong central government".
Most Kurdish parties want a federal structure in Iraq
That is not what the Supreme Council for the Islamic Revolution in Iraq has in mind.
It is a Shia party with strong links to Iran.
Its leader, Abdel Aziz al-Hakim, wants to take over the south, "to guarantee the future for our sons and grandsons".
He said that a strong Shia region bringing together the nine provinces south of Baghdad was important "to stop injustice coming back".
The Supreme Council for the Islamic Revolution in Iraq has its own militia, the Badr brigades, who have been fighting for influence with the other main Shia militia, the Mehdi army, led by Moqtada al-Sadr.
This fight also extends to disagreements over federalism.
Moqtada al-Sadr wants to keep the nation united and has found some common cause with leading Sunni groups in this.
One compromise plan being proposed is to allow regions to develop some autonomy, but not to group together into blocks of more than three provinces and not to allow security to fall from the hands of central government.
The fear of Shias outside the militant blocs is that the creation of a Shia state in the south would abandon Shias elsewhere in the country.
One of the leaders of the al-Fadhila (Virtue) party, Mukhles al-Zamal, said that the plans for the south amounted to creating "an oil emirate".
And he said the move would accelerate the displacement of people out of mixed communities.
The Iraqi government believes that about 200,000 people have already been forced out of their homes, in a process that has accelerated since the destruction of the Shia mosque in Samarra in February.
The Mehdi army of Moqtada al-Sadr, who wants a united Iraq
The Iraqi authorities believe that the attack was carried out by al-Qaeda in Iraq, presumably to foment just the kind of sectarian unrest that now threatens to destabilise the state.
As MPs discuss the federal issue, they know as well as anybody the threat of civil war looming over their proceedings.
Some kind of law allowing a federal structure for Iraq is bound to emerge, since there is a majority for it among Shia and Kurdish parties, but the exact shape of the new state has still to be agreed.
And then there is the issue of the status of Kirkuk amid the rich northern oilfields, also left unresolved in the new constitution and subject to a referendum.
If the Kurds succeed in bringing it into their area, then that will leave the Sunni-dominated central region with little more than Baghdad and the desert.