The Ulster Unionist Minister, Sir Reg Empey, has warned that unless the governments' proposals deals satisfactorily with decommissioning it will be unacceptable.
Sir Reg, currently acting as First Minister following Mr David Trimble's resignation, said his party was not prepared to allow Sinn Fein continue in ministerial office while the IRA broke promises on arms.
"If the proposed package does not deal with the decommissioning issue effectively, then it is unacceptable," he said.
Commenting on a report in The Irish Times yesterday detailing likely elements of the package, the UUP Assembly member, Mr Fred Cobain, said it represented further appeasement of republicans. "If this is the take-it-or-leave-it package then I think the Ulster Unionist Party will be leaving it," he said.
"Both prime ministers should think very carefully about how they proceed in the next few days. They could be on the brink of destroying everything," he added.
A report in yesterday's Irish Times said likely elements of the package included an indemnity for paramilitaries on the run, an international judge to examine a number of controversial killings, legislative change to enact police reform and movement on how arms could be put beyond use.
The Ulster Unionist MP, Mr Jeffrey Donaldson, said the package briefed to the media was "way wide of the mark" of what could be accepted by his party.
He said no further significant concessions on policing could be agreed by the UUP and he firmly ruled out an amnesty for paramilitaries on the run, because it was not in the agreement.
"I can't be categorical but I believe we're probably looking at suspension and another review," he added.
Mr David Ervine, of the Progressive Unionist Party, said the proposals would be "a waste of space" unless there was a "clear, unadulterated" statement of intent for the future by both sides.
He said questions his party posed to Sinn Fein at the recent Weston Park talks remained unanswered, and his community had diminished confidence in republicans' motive in the peace process.
Mr Gary McMichael, of the Ulster Democratic Party, said the British government was "caving in" to republicans' demands without any clear reciprocation.