The Green Party leadership is to recommend supporting next year's European Union referendum to members when they meet to decide the party's stand next month.
Under party rules, two-thirds of the members will have to vote Yes if the Greens are to support a European referendum for the first time in their 25-year history.
Equally, anti-referendum campaigners within the party, such as ex-Green MEP Patricia McKenna, will have to get a two-thirds majority to swing the party behind a No campaign.
If neither motion secures the necessary majority, delegates will be asked to support a third resolution to ensure that the Greens back the holding of a referendum.
Party leader John Gormley had wanted more room for manoeuvre in the event that the party failed to back either course, but he was rebuffed by party councillors, The Irish Times understands.
At a meeting with councillors in early October, Mr Gormley had proposed that a referendum would be held - where votes can rank options according to their preference - if both positions were defeated.
Under this plan, Green delegates would have been asked to decide whether the party should campaign in any way if they could not decide on a clear Yes or No stand.
In addition, delegates would have been asked if they wanted party funds spent on either side of the campaigns that will be undertaken before the referendum is held next summer.
However, this course was rebuffed "nearly unanimously" by councillors when they met in Aherlow in south Tipperary in early October, sources said.
Information packs on the EU reform treaty, which have been drafted by the party's European affairs committee and which do not come down on either side of the argument, will be sent to party members next week.
Last night the Greens insisted that a decision to back the No campaign, or the inability to decide one way or the other would not hurt relations within the Government.
"The treaty is not part of the programme for government. There is no question of it being a make or break issue for the Government," said the party's spokesman last night.
However, he cautioned against predictions that the party would oppose the treaty or be unable to make up its mind: "Let's just wait and see, shall we?" he said.
"We expect that there will be a vigorous debate. The Green Party . . . has always had a comprehensive and informed debate on EU issues," he said.
Deputy party leader Mary White said she expected that "the nuances" of the motions to be put to the conference would reflect the fact that the party was now in Government.
Minister for Communications, Energy and Natural Resources Eamon Ryan has indicated that he wants the party to back the Yes campaign, while Senator Deirdre de Burca has indicated that she will do likewise. The party did hold a number of consultation meetings on the terms of the now defunct constitutional treaty last year.
Support for a Yes vote was evident from younger and newer members of the party, though the older wing was still uncomfortable.
