The Amalgamated Transport and General Workers' Union, one of the country's biggest unions, has decided to call for a No vote in the upcoming referendum on the Nice Treaty.
The union's Irish head, Mr Mick O'Reilly, said the treaty would interfere with Irish neutrality, create a two-tier Europe, hinder relations with Northern Ireland and affect the protection of public services.
The union, which has a longstanding neutrality policy, said it viewed with alarm plans to co-ordinate better the European Union's military arrangements. Under the treaty, Irish forces could be deployed up to 4,000km outside the EU's borders, "opening up the possibility of Irish military participation in conflicts in Africa, the Middle East and Eastern Europe".
Furthermore, the EU's Rapid Reaction Force had "real and identifiable" links with NATO, Mr O'Reilly said yesterday. "The RRF is not a wholly `European', `EU' force," he said.
The Swedish EU Presidency has had to change its plans to develop the EU's crisis management forces because of the EU's need for access to NATO's military assets, he said.
"All of the above puts into contrast the Taoiseach's insistence that foreign and defence considerations in Nice are minor details," said Mr O'Reilly, a longstanding opponent of Ireland's involvement in the EU.
Unlike Sweden, the Irish Government has not been honest about the changing face of military neutrality, he said. "It is imperative that we have an open and honest debate."
He continued: "The Swedish Prime Minister, Mr Goran Persson, has faced up honestly to the military implications of the Nice Treaty by seeking an end to his country's neutrality, saying: `When we don't have a Cold War and we don't have two superpowers opposing each other, neutrality is not a relevant concept.' " "Instead, the Irish Government has engaged in misleading information," said Mr O'Reilly.
He said there was nothing in the Nice Treaty that insists upon the authorisation of the United Nations before EU troops can be deployed.
"This Government's policy declaration cannot bind future governments.
On Northern Ireland, he said the ATGWU, which has a sizeable membership on both sides of the Border, is concerned that the treaty could create a two-tier Europe.
"We would like to see made public any sustained study the Irish Government may have undertaken in relation to the issue of enhanced co-operation," he said.
A union policy document stated: "Since its foundation, the European Union has been based on the principle of unanimity and equality regarding major constitutional-legal-political developments.
"Neither the euro nor the Rapid Reaction Force could have come into force without this unanimity, despite the fact that several countries did not immediately join in these developments. This unanimity will be undermined by the Nice Treaty's concept of enhanced co-operation, which allows, through qualified voting, a number of countries to proceed despite the opposition of other countries.
"While qualified voting exists in a number of policy areas, this is qualitatively different insofar as it affects the very nature of the EU's institutions and, so, qualifies member-states' participation."
The union conceded that the loss of a commissioner after the EU expands beyond 27 members may be "a practical necessity", and the reweighting of votes may be demographically fair. But it added: "It is difficult to justify these developments without greater accountability and transparency through a greater role for the European Parliament, or member-states' parliaments."
