The Green Party will have to consult party members before deciding its stand on a new EU treaty in advance of a referendum to be held before the end of next year.
EU leaders, including Taoiseach Bertie Ahern, negotiated until 5am on Saturday on terms of reference for a new treaty.
Talks on the shape of the final text will begin in July under the incoming Portuguese EU presidency. Lisbon hopes these will end by October, with the treaty ratified by all member states before the 2009 European Parliament elections.
Acknowledging that the Greens would not oppose a treaty, former Cork South Central Green TD Dan Boyle said the party may well "seek not to influence a decision and leave it to voters to make up their own minds", although this position would be difficult to maintain given the Greens' place in power.
Asked if Ireland could win a referendum, German chancellor Angela Merkel, who led the Brussels talks, said: "I assume if there is a referendum in Ireland we will be successful." Asked if the process of ratification would be stopped in its tracks if Ireland voted No, she said: "No comment, because that is hypothetical."
Faced with Polish opposition, the leaders agreed that EU states would hold on to their existing vote shares until 2014, rather than 2009, and until 2017 if a member state insists.
"It is an issue not even about votes," Mr Ahern said after the talks ended. "It is about history, it is about the war, it is about how they are treated by their neighbours. It is about respect. It is not actually about numbers."
The Government has already said it is "likely" that a referendum will be held, because it had previously been advised that one would be necessary if the original EU constitution agreed in 2004 had been put to the people.
"At the end of the day, 90 per cent of what was in the constitution is still there. I make no secret of the fact that I would rather the form that was set out. We were not going to get it the way that we wanted it, so we had to go back and look at the issue," the Taoiseach said.
Plans to include references to an EU flag and anthem had been dropped because they carried unacceptable symbolic value for some EU states, even though Mr Ahern said he believed they did not affect member states' rights.
"Beethoven is out and the flag is out. I don't think that will make a damn difference to anyone in Europe. I don't think anyone will move it off their cars and their flags, but it does make people feel better that it is out of the constitution. That makes them feel better, so I am thrilled and ecstatic for them," he told The Irish Times.
