Both the UUP leader, Mr David Trimble, and his chief opponent have written to delegates to the ruling Ulster Unionist Council outlining their significant differences in bids to win support, writes Dan Keenan, Northern News Editor.
Mr Jeffrey Donaldson has made his pitch by pointing up what he sees as losses in party support which he blames on flawed leadership decisions since the Belfast Agreement was signed in 1998.
"The Ulster Unionist Party began this process with 10 MPs and some 200 councillors," he wrote. "Five years later, we are reduced to six MPs and some 150 councillors. We have little to show for the price we have paid.
"We have failed to achieve our twin objectives of devolution and decommissioning. The Assembly is prorogued, the elections cancelled and the decommissioning process has become a farce without a single paramilitary group co-operating with the Independent Commission."
Mr Donaldson then targets the governments' Joint Declaration drawn up at Hillsborough in April. His motion, to be considered by the UUC this evening, calls for its rejection on the basis that it represents a departure from unionist principles.
"The Joint Declaration is packed with concessions to Sinn Féin/IRA," wrote Mr Donaldson, "and offers little prospect of delivering on stable devolution or credible decommissioning. It does not provide the best way forward and should be unequivocally rejected by the UUC." He ends ominously: "This is surely a defining moment."
Mr Donaldson's letter also lists "10 reasons to reject the joint Declaration".
These criticise the declaration for not containing a timetable for decommissioning and complete disarmament of paramilitary groups. It further criticises the document for not requiring paramilitaries to disband and for allowing the Irish Government a "significant role for the first time in the internal affairs of the Northern Ireland Assembly and can even propose sanctions against the UUP".
Mr Donaldson also claims the Assembly cannot exclude republicans from office without the support of the SDLP, and removes the power of suspension from the British government.
He also states that "normalisation" moves will mean the end of military bases in Armagh and Fermanagh and leave only one in Co Tyrone. He claims that, despite last week's statement by the British Ministry of Defence, there is no long-term commitment to the home elements of the Royal Irish Regiment.
Mr Trimble has countered in his letter to delegates.
"I recognise and share many of the concerns about the Joint Declaration," he writes.
He goes on to explain that he established a comprehensive review procedure to consider the document. Calling for a cherry-picking approach, he asks delegates to accept that it would be a tactical mistake to reject all of the Joint Declaration at this time.
"I do think it is a pity that we could not continue to work things out quietly within the party," he writes. "Our supporters have been faced yet again with the unseemly sight of the party tearing itself apart."
He claims successes in "putting republicans on the spot" through a tighter definition of paramilitary ceasefire and through sanctions on parties linked to paramilitaries who are held to be in default of their responsibilities.
"Our government has now agreed to legislate for new powers to impose sanctions. The significance of this can be seen from the very last sentence from the relevant paper."
In direct contradiction of claims by Mr Donaldson, he goes on: "This power would be vested in the British government alone. Its exercise by the government could not be blocked by the need for cross-community support. There are fears that the procedures give the Irish Government power over internal Assembly matters. This we will oppose: there must be no breach of British sovereignty."
He concludes: "Let us put the pressure back on republicans. Let us have the confidence in ourselves, in our ability to work at our problems. Let us resolve to work better, to stop continually dividing the party in public. Let this be an end to these requisitions."