David Trimble's most strident opponent, Jeffrey Donaldson, is warning that unionists face the prospect of Sinn Fein becoming the North's largest party.
The warning comes ahead of a flurry of activity on both pro and anti-Agreement sides of the UUP in the run-up to the party's ruling council meeting this weekend.
Mr Donaldson is calling on party members to apply sanctions against Sinn Fein over alleged breaches in the IRA ceasefire.
Although he insists he will not contest the leadership of the UUP, he further states that continuing to co-operate with Sinn Fein in the North's Executive is untenable.
Mr Trimble, however, is calling on the party to rally around him, saying they must remain acutely aware of public opinion.
He says that the establishment of a monitor of paramilitary violence will serve as a watchdog, and will force British Prime Minister Tony Blair to act if the IRA are found to be active.