The Treaty of Nice militarises the European Union and should be opposed, the Sinn Fein TD, Mr Caoimhghin O Caolain, said yesterday.
The Cavan-Monaghan TD was speaking at a press conference organised by the Peace and Neutrality Alliance, which said debate on the treaty had been "totally inadequate".
A statement of support for the alliance was issued by Mr O Caolain, the Independent TDs Mr Tony Gregory and Mr Seamus Healy, Mr Joe Higgins of the Socialist Party, and the Green Party TDs, Mr John Gormley and Mr Trevor Sargent.
"As supporters of Irish neutrality we are united in our opposition to the Treaty of Nice.
"Already the Government has involved the State in NATO's PfP without a promised referendum, and in the ERRF, the EU army, control of which is with the EU Council of Ministers and the EU Political & Security Committee," it said.
They announced what they called the 25th Amendment to the Constitution Bill, the Neutrality Bill, which the alliance drafted and which is co-sponsored by the TDs.
It seeks to amend the Constitution to include the guarantee that the State "shall maintain a policy of non-membership of military alliances."
Mr Higgins said the Government was trying to slip through a referendum without the real implications being properly delineated.
"The reality is that some of the more powerful states in the EU want to move to have a military wing to rival that of the United States.
"They wish to be able to dictate to neighbours on the fringes of the expanded EU and carry weight with countries much further afield," he said.
This was the only explanation for the creation of a 60,000strong "so-called" rapid reaction force, capable of being deployed over a wide area, he said.
The alliance chairman, Mr Roger Cole, asked all members of the Oireachtas to support the amendment ensuring non-membership of military alliances.
"Successive EU treaties have eroded Irish neutrality. It must now be protected constitutionally," he said.
"The Treaty of Nice is just another attempt to erode Irish neutrality. Now is the time to end the erosion as we are integrated in the new European empire. The Bill provides the opportunity for TDs and senators to show their opposition to the militarisation of the EU."