The Irish Alliance for Europe has stated that the Nice Treaty is only about one issue - EU enlargement.
The group, which is campaigning for a 'yes' vote in Saturday's referendum, said concerns about militarisation, privatisation, immigration, neutrality and democracy are all "red herrings" and distortions raised by people opposed to the Treaty.
Speaking at one of the alliance's press conferences today, former president Patrick Hillery said a 'no' vote could lead to a rise of aggressive nationalism in former Soviet states.
Former Taoiseach and Fianna Fail leader Albert Reynolds said the Irish electorate should repay the generosity shown to Ireland by other EU members in the past.
Sinn Fein has rejected the alliance's claims about the treaty and said the issues of neutrality, democracy and Irish independence are central to Saturday's referendum.
Party spokesman Caoimhghin Ó Caolain said Sinn Fein is campaigning for a "no" vote because it wants to see a Europe of equals, not a two-tier EU.
He also said that if the Nice Treaty was only about enlargement, the Irish people would not have to vote on it.
"Nice, in our view and in the view of other campaigning parties and groups, is about the governance of the European Union and not about enlargement," Mr ÓCaolain said.