The Government has published the wording for the second referendum on the Nice Treaty, which includes a prohibition on Ireland entering into a common EU defence policy.
However, the Government could still approve the establishment of a common EU defence, excluding Ireland, in the same way that the euro was introduced.
All 15 member states agreed to the introduction of the new currency, even though three countries decided not to take part.
The Government says this gives constitutional effect to its declaration at Seville that a referendum would be held on any participation in a common EU defence.
The wording has been welcomed by Fine Gael and Labour, but the Greens, Sinn Fein and the Socialist Party have said it changes nothing.
Earlier the Taoiseach told the Forum on Europe that the EU would face an unprecedented and unpredictable crisis if Ireland rejected Nice once more. That would not be in Ireland's interest, he said.
Mr Ahern said it would be a terrible event if the country were to vote no. It would, he said, be a kick in the ankles to the applicant countries who had worked so hard to join the EU.
Denmark's Prime Minister Anders Fogh Rasmussen warned last night that if Ireland were to reject the Nice Treaty a second time, the entire EU enlargement project would be thrown into confusion.
Ratification of the Treaty is due at the end of this year, failing which many provisions cannot come into effect.
