Ulster Unionist leader David Trimble is facing a vote of no confidence in him as Member of Parliament for the Upper Bann constituency.
Mr Trimble and Jeffrey Donaldson both face no-confidence votes
Party members in the constituency are seeking an extra-ordinary meeting of the party's local association to vote on the matter.
The move comes as Mr Trimble prepares to face down critics in the party's ruling council next week.
Sceptics within the Upper Bann Ulster Unionist Association say they have 25 signatures, which they claim is enough under party rules to require the meeting to be held.
They say they believe the meeting will be held within the next two weeks.
Earlier this week, Mr Trimble met his constituency colleagues to discuss ongoing concerns about party policy.
His failure to reassure some members has left him facing the vote.
Robert Oliver is behind a petition to force Mr Trimble's resignation as MP for Upper Bann.
"David Trimble as an MP has carried out as exceedingly good work over the years and no one can fault him in that," he said.
I have always had the over-whelming endorsement of my constituency association in Lagan Valley and I cannot see that changing
"What David Trimble has not been doing in the past five years is listening to a large percentage of the people who put him where he is today and when you start doing that and start neglecting those people, then the snake will bite."
Meanwhile, members of the Ulster Unionist Association in Lagan Valley have presented a 70-strong petition seeking a vote of no confidence in their MP Jeffrey Donaldson.
Ivan Davies said he was one of 10 councillors who have signed the petition.
"Some people in the Lagan Valley constituency have been growing increasingly concerned that Jeffrey has not been accepting the democratic decisions of the Ulster Unionist Council," he said.
"This is the 11th meeting we will have had and they have become a little fed up to be quite honest."
Responding to news of the vote, Mr Donaldson said he had no doubt he would be supported by his constituency association.
"I have always had the over-whelming endorsement of my constituency association in Lagan Valley and I cannot see that changing," he said.
The motions follow the latest wrangle between the two MPs which is due to take centre stage at a meeting of the party's ruling council next week.
The British and Irish Governments' joint declaration and the future of the Royal Irish Regiment is likely to dominate the meeting next Monday.
Last month's joint declaration outlined plans to reduce troop numbers to 5,000 as part of an attempt to move the political process forward in Northern Ireland.
MoD sources have played down reports that this could mean the complete disbandment of the Royal Irish Regiment's three home battalions, emphasising no cuts would be made until the IRA declared its war was over and decommissioned its weaponry.
Mr Trimble urged anti-Agreement Mr Donaldson to withdraw his requisition to call for a meeting of the party's ruling council.
Delegates will be asked to decide on a motion calling on them to reject the governments' joint declaration and save the Royal Irish Regiment.
Mr Trimble said an emergency executive meeting had already been called for 6 June, which made the Lagan Valley MP's move "redundant".
However, Mr Donaldson insisted he believed the threat to the regiment, taken alongside the other proposals contained in the joint declaration, was so serious that a council meeting was necessary.
The joint declaration included five annexes dealing with security normalisation, policing and justice, human rights and equality, on-the-run paramilitaries and mechanisms to verify and monitor any deal.
Last month, two Army watchtowers were taken down near the border in south Armagh as part of the joint declaration.
Northern Ireland's devolved administration was suspended last October amid allegations of IRA intelligence gathering in the Stormont government.
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