FINE GAEL and Labour are to oppose the formation of a key element of the Government's plan to deal with the outcome of the Lisbon Treaty referendum defeat.
The development fractures the cross-party unity that has existed on European Union issues between the major parties, as both main Opposition parties adopt a slightly more distanced attitude towards the treaty.
Minister for Foreign Affairs Micheál Martin last week proposed the creation of a special Oireachtas committee to hear evidence on the outcome, and on possible next moves.
Last night, however, Fine Gael leader Enda Kenny issued "a preliminary response" to Mr Martin in which he said a special body was not needed, and that the work should be done by existing Oireachtas committees.
The Labour Party said it would issue its response to Mr Martin next week, but a spokesman said it had "yet to be convinced of the value" of the proposed committee's work.
During talks with Opposition leaders and party representatives last week, Mr Martin suggested that the Oireachtas should be recalled for a day in early September to agree on its establishment.
The significance of the Fine Gael move is a strong signal that it is less likely to be as supportive to the Government on EU issues in future, particularly since half of its declared support voted No in June.
The Labour Party leader, Eamon Gilmore, who has already said that he would oppose a second referendum, is faced with the reality that a strong majority of his party's support base voted No.
The Oireachtas committee, which would be chaired by an Independent, would have reported later this year, before the December EU summit.
In a separate development, Luxembourg prime minister Jean Claude Juncker yesterday predicted that Ireland would get declarations from other EU states on abortion, neutrality and corporation tax, as happened after Ireland rejected the first Nice Treaty referendum.
However, the declarations would not be included in the text of the Lisbon Treaty itself, he said, since this would mean that ratification would have to happen all over again in the other member states.
Downplaying any prospect of a quick solution, Mr Juncker - the EU's longest-serving head of government - said he believed the crisis caused by the Irish No would not be solved quickly.
In an interview with the Vienna-based Kurier newspaper, he said the French EU presidency must "make clear" under which conditions the Irish could vote again.
"My sense of reality tells me that the Lisbon Treaty will still not be in force in the middle of 2009. I fear that the Irish people would view another referendum in the spring as a surprise manoeuvre," he said.
Asked what could be offered to Irish voters to persuade them to vote Yes, Mr Juncker said: "A very clear decision of the European Council that nothing will be touched in relation to neutrality and the abortion and tax regimes of Ireland."
However, he said "all" of Ireland's concerns "which led to the No vote" had been answered during the negotiations on the treaty itself.