The Ulster Unionist leader, Mr David Trimble, is facing an uphill battle to be re-elected as the North's First Minister after a member of his Assembly team, Ms Pauline Armitage, said she would vote against him.
Mr Trimble needs the support of every member of his Assembly party if he is to regain his former position as head of the power-sharing Executive. He is expected to put himself forward for re-election at an Assembly meeting on Friday.
Ms Armitage, who opposes the Belfast Agreement, last night told The Irish Times she could not support him. "At this stage, I have to say I am planning to vote against David Trimble. I have not received the assurances I require on decommissioning. The vote isn't until Friday but I think it would take a miracle for me to receive all the necessary assurances by then."
The support of another UUP Assembly member, Mr Peter Weir, is also in doubt.
Under the Assembly's rules, Mr Trimble needs the backing of both a majority of nationalist and unionist members. While the votes of SDLP and Sinn FΘin members are guaranteed, the defection of even one UUP member would be enough to divide the unionist camp evenly - 29 to 29 - and prevent Mr Trimble's re-election.
In that event, the Northern Secretary, Dr John Reid, would have to decide whether to suspend the Assembly or call fresh elections.
A meeting on Saturday of the UUP's 110-strong executive endorsed Mr Trimble's plan to return to government with Sinn FΘin and called on all the party's Assembly members to support him.
There has been speculation that, if Mr Trimble fails on Friday, Dr Reid would suspend the Assembly to allow the Women's Coalition to "redesignate" as unionist in order to support Mr Trimble during another vote. However, such a move could seriously damage the credibility of both the UUP leader and the political institutions.
If both Ms Armitage and Mr Weir voted against their party leader, the support of the two Women's Coalition members would not be enough to re-elect him. Mr Trimble said he wanted to be re-elected credibly and was not seeking other parties to redesignate.
"We are going into this hoping to be elected, expecting to be elected on unionist votes. The stakes are high. The margin I dare say might be narrow, but it has been narrow before and, in the famous words of Harold Wilson, 'One vote is enough'."
Ms Armitage said: "My problem is not with David Trimble personally but with his policies. Decommissioning was meant to have been completed by May 2000, according to the Belfast Agreement, but it is only beginning now and too many questions remain unanswered. We don't know how many weapons were decommissioned and how or where it was done."
Ms Armitage said she also required details of plans for future IRA disarmament.
"We have had a programme for demilitarisation. We have had a programme for the reform of the RUC. We need a programme for decommissioning too."
The DUP deputy leader, Mr Peter Robinson, predicted that Mr Trimble would not be re-elected First Minister on Friday and said there was a strong possibility of fresh Assembly elections.
Mr Robinson said he had told his party to prepare for an election campaign. "Even Trimble knows he is beaten. I don't believe that, without cheating, there will be a vote in favour of David Trimble, and by cheating I mean getting other parties to redesignate.
"The DUP has moved over the weekend to get other things in place for an election," Mr Robinson said, " such as preparing our manifesto and strategy."