Anti-Agreement Ulster Unionist Party MLA Ms Pauline Armitage has called for a review of the Belfast Agreement adding her party leader Mr David Trimble has made too many concessions to Republicans.
Mr Trimble is facing a new challenge to his decision to return to government with Sinn Féin following the beginning of IRA decommissioning last week.
The IRA announced last Tuesday that it was beginning the process of disarming to save the peace process. The Independent International Commission on Decommissioning confirmed the move.
Ms Armitage told RTE's Morning Ireland she was "quite likely" to vote against Mr Trimble on Friday when he stands for re-election as Northern Ireland's First Minister.
"He has made far far too many concessions to Sinn Fein/IRA and I also believe he has given far too much input from the Republic of Ireland into this part of the United Kingdom", Ms Armitage said.
Another anti-Agreement Ulster Unionist Mr Peter Weir is also likely to vote against Mr Trimble. Both have said they will not abstain in the vote.
Ms Armitage added: "I personally believe we are under now joint authority. I don't accept that. At every turn Mr Ahern has something to say".
She said she did not doubt that some IRA decommissioning took place.
"I think the public should know what exactly was destroyed."
"We don't know what has happened to these weapons or how many."
"The event was significant, but that doesn't mean the actual numbers are significant", she said.
Asked what a vote against Mr Trimble was likely to achieve she Ms Armitage said: "What I want - I want a review of the Agreement. This Agreement does not have the support of the unionist people and that was proved at the election.
She went on to say that, while she did not agree with it, she could understand why violence was taking place in North Belfast because of anger and frustration at the Belfast Agreement which did "absolutely nothing" for unionists.
