The Peace and Neutrality Alliance said that the Amsterdam Treaty threatened to replace Ireland's neutral stance with a policy of common defence with other EU states.
The treaty envisaged the integration of the nuclear-armed Western European Union into the EU, involvement in "peacemaking" and co-operation with the European arms trade, according to the organisation.
Socialist Party TD Mr Joe Higgins said the intention of the treaty was to move towards a common EU defence force, an EU armaments industry and armed intervention for "crisis management".
"Irish people can't rely on the spin put on the treaty by Mr Andrews. The Irish people have to rely on the written word which is down in black and white," he said.
Mr Roger Cole, chairman of the Peace and Neutrality Alliance, said the organisation was campaigning for a "no" vote in the referendum so that the treaty could be renegotiated and articles affecting neutrality changed.
Referring to a report in last week's Irish Times about the wording of the referendum poll, he said it appeared the Government could make further defence commitments with the EU without another referendum taking place.
"The Government is advocating that this be put into the treaty. They are saying they want to have a common defence policy," said Mr Cole.
In an MRBI poll conducted in September 1996, 69 per cent of people said they believed Ireland should maintain its policy of neutrality, while 20 per cent said they believed it should be changed.
Mr Cole said the organisation believed there remained a role in the 21st century for "small, independent, democratic, neutral states" which would not be regions of nuclear armed superstates, European or otherwise.
Former Workers' Party leader Mr Tomas Mac Giolla said that Irish people were constantly told there was no tradition of neutrality in the Republic, but this was untrue.
The Irish Parliament voted almost unanimously to stay out of the first World War, he said, and Sinn Fein won the 1917 election on its anti-conscription campaign.
Mr Sean Crowe, spokesman for Sinn Fein on the issue, praised the Peace and Neutrality Alliance for its opposition stance in the referendum campaign and said it was vital to halt the erosion of Ireland's neutrality.
"It was Wolfe Tone who first made the case for an independent Irish foreign policy and this has been a principle of all the most progressive movements in Irish history," he said.
"It is a policy which the Irish people support overwhelmingly and that is why the Government and those parties who want us to approve the Amsterdam Treaty are so anxious to convince the people that neutrality is not under threat."