UUP leader David Trimble says the Northern Ireland Assembly is on course to collapse before the end of next weekend.
Mr Trimble says the assembly will not survive if a bid to oust Sinn Fein from power fails.
He said alleged Republican involvement with Colombian guerilla group FARC had "crystallised" Unionist opinion against Sinn Fein.
He said of the exclusion motion: "If that does not achieve cross-community support then we will have created a situation where it would be impossible for Ulster Unionist ministers to continue in administration".
Mr Trimble added: "We are now coming to a situation where the probability is that the Northern Ireland administration will cease to be some time next week.
"It is a matter of sadness for me that this has come. We have put awful amount of effort into trying to make the (Good Friday) Agreement work.
"Regrettably, those efforts on our part have not been matched by similar efforts by the Republican movement."
Mr Trimble said that, despite 17 months of power-sharing at Stormont, there had still been no hard-evidence of decommissioning of IRA weapons.
He said: "We have been incredibly patient. We have waited and waited. And I think for most Unionists the crystallising moment was the discovery of the extent of the IRA's involvement with some of the nastiest paramilitaries in the world, I'm thinking here of FARC."