Delegates to Monday's Ulster Unionist Council meeting receive official notice today of Mr Jeffrey Donaldson's motion and of amendments to be tabled by Mr David Trimble. They will also receive a letter from the party leader.
Mr Trimble was considering yesterday whether to make a statement, as key supporters expressed quiet confidence he would win any vote on the two governments' Joint Declaration.
However, there was no attempt by some well-placed unionist sources to play down the bitter nature of the increasingly personal divisions between the pro- and anti-agreement elements within the UUP.
"It's just a mess," said one, while another forecast that if Mr Trimble wins on Monday, people will leave the party.
The Irish Times was told that the motions of no confidence against both Mr Trimble and Mr Donaldson, filed by members of their respective constituency unionist associations, had added a new bitterness to the exchanges between the party's two wings.
Some 80 members in Mr Donaldson's constituency have indicated no confidence in him while around 25 members in Mr Trimble's Upper Bann constituency have done the same against their leader. Some of these are elected representatives.
One source all but ruled out any compromise motion at Monday's UUC on the grounds that no one would buy it. "It's got very acrimonious, to a level that has not been seen in the party since 1973. It's really nasty stuff."
The UUP executive meets today and will have, for the first time, an opportunity to discuss the overall political situation and the party's internal divisions. This could prove to be a form of dress rehearsal for the Monday meeting of the UUC's 860 delegates.
The split now appears so fundamental that resolution can only follow outright defeat for one element or the other. "One way or the other, something's got to give on Monday. I don't know what that is yet, but I can't see how you square the circle on this split at the moment," one source said.
Mr Donaldson, the de facto leader of the anti-agreement wing of the UUP, has made his position regarding the Joint Declaration and the position of the current leadership unequivocal.
He regards the Joint Declaration as a fundamental breach of unionist principle and views the last five years of the leadership to have been a series of cheap concessions.
Last night he repeated his claim that he would have to consider his position in the event of a defeat on Monday.
Refusing to elaborate on what precisely "considering" means, Mr Donaldson stated: "If the UUC in any way endorses or prevaricates on the Joint Declaration, including a role for the Irish Government in the internal affairs of the Northern Ireland Assembly, that is a key issue of principle for me as an Ulster Unionist. In this circumstance I would have to consider my position. I have nothing to add to that."
He said this was not about tactics or scare-mongering. "It's about integrity, it's about honesty, it's about clarity." Having voiced support for initiatives fostering greater unity among unionists of various parties, Mr Donaldson seemed to be supported by Mr Robert McCartney of the United Kingdom Unionist Party, who said yesterday he would consider joining a party or working alongside one "that had not dissimilar objectives" to his own and other anti-agreement figures.