A marathon session is expected when members of the Ulster Unionist Council meet today for their crunch decision on the peace agreement reached at Stormont last week.
Supporters of the UUP leader, Mr David Trimble, were confident last night that he would get the backing of a majority of the 858 members, but further evidence emerged of serious divisions within the party.
Mr John Hunter, a member of the Northern Ireland Forum, said he had never seen such division.
"Lifelong friends are split, council colleagues are split, even Forum group members are split.
"My great fear is that unionism has the potential at this time to literally pull itself apart," he said.
The party's deputy leader, Mr John Taylor, said he was confident the council would back the deal.
There was a very healthy debate taking place within the party because people realised they were facing a historic decision.
"It is quite obvious that ordinary unionists on the street are behind this," he said.
Mr Trimble received another blow yesterday when the Orange Order in Co Armagh, which is in his own constituency, rejected the agreement and called on him to reconsider his support for it. The order's 7,000 members in the county were told to study the document and vote with their conscience.
The County Grand Master, Mr Denis Watson, said the document was "hard to stomach", adding: "We cannot countenance prisoners being released in such a short time-scale and also members of Sinn Fein/IRA sitting down and taking decisions relating to the governance of our province."
Mr Trimble is being backed by just three of his MPs: Mr John Taylor, Mr Ken Maginnis and Mr Cecil Walker. Mr Jeffrey Donaldson has said he opposes the agreement but is still supporting the party leader. The five remaining MPs are opposed to the deal.
Sources close to Mr Trimble said they believed they could get the backing of 70 per cent of council members, but this was the most optimistic view. Others believed it would be closer to 60 per cent.
"The fact is that the parliamentary party has never been representative of the party overall," said one, claiming that most constituency associations were backing the agreement.
Supporters of Mr Trimble are taking solace from the fact that when he was elected party leader in 1995, more than 75 per cent of council members voted for either Mr Trimble, Mr Maginnis or Mr Taylor, who are now united behind the deal.
The British Prime Minister, Mr Tony Blair, attempted to reassure unionists about certain aspects of the agreement in an interview on BBC radio yesterday evening.
He said he understood people's concerns about the early release of prisoners. Prisoners would only be allowed out if they had demonstrated a commitment to a lasting peace, and they would then be on licence.
"It is only in the context of a genuine, lasting peace that there is any question of early releases taking place."
He said there was a clear provision in the agreement that someone could be removed or excluded from office in the Assembly if their organisation was committed to, or preparing for, violence.
Mr Blair said there was no question of the RUC being disbanded or of former paramilitaries taking up a policing role. However, it was hoped that in the future the RUC would attract people from all sides of the community.
The Royal Mail yesterday started delivering the agreement to households around the North.