Sinn Féin would lead "a major campaign, north and south" to oppose ratification of the EU constitution, Dublin MEP Mary Lou McDonald told a special conference organised by the party in Dublin at the weekend.
Describing the constitution as "without doubt one of the most important issues facing Ireland today", Ms McDonald said that, if ratified, it would "mark an important shift in our relationship with the EU".
Sinn Féin believed broad public debate was "absolutely essential" and had organised the two-day conference precisely for this purpose. "After this event, we will initiate a nationwide series of events and activities to provoke discussion and debate."
It was not a question of being for or against the EU: "Our approach to the EU is one of critical engagement, those things that are in the interests of the Irish people we support and seek to further; those things that are not, we oppose and campaign to change," Ms McDonald said.
Ms Lilian Halls-French, of the European Feminist Initiative Against the Constitution, said the document reflected a "patriarchal and neo-liberal" approach and "confirms the subordination of women".
The constitution promoted the dismantling of public services which were mainly relied upon by women. It was also socially regressive. "The constitution project marked by the refusal to harmonise rights to contraception, abortion, divorce," she said.
Green Party councillor Deirdre de Búrca complained there was "less and less tolerance" for those who questioned the current direction the EU was taking.
"A broad progressive movement, largely of the left, is emerging across Europe that is very pro-European but critical of the neo-liberal direction of the European Union."
The constitution should be rejected because it "enshrined many elements of the neo-liberal economic agenda".
Instead of the "centralisation of power" proposed by the constitution, there should be "a truly multi-level system of governance for the EU", Ms de Búrca said.
Sinn Féin TD for Dublin South-Central Aengus Ó Snodaigh said he was opposed to the constitution "because it repackages the EU as a military and economic superpower" and the world did not need more superpowers or military alliances.
Sinn Féin believed "another EU is possible", Mr Ó Snodaigh said. "We are firmly opposed to the federalist agenda, but we also have our own positive vision for what the EU could be. We have an agenda for radical change at the European level."
Several speakers complained of widespread bias and imbalance in coverage of EU affairs by the Irish media.