The employers' lobby group, IBEC, has called on the leaders of the four largest political parties in the Dail to meet immediately to agree a national response to the "crisis" in our relations with the EU.
IBEC and other business organisations and companies, including the American Chamber of Commerce and AIB, have warned that the No vote on the Nice Treaty is very bad news for Ireland economically and politically. Market analysts also warned that the vote will further undermine the euro on the foreign exchange markets.
IBEC insisted that the vote was "an Irish problem, of Irish making, and which Ireland alone is going to have to solve".
According to Mr Jerry McCrohan, president of the American Chamber of Commerce, the vote is likely to have little short-term impact on US investment. But he warned that if the argument is not turned around, there was a danger that Ireland could be perceived as being anti-globalisation.
"A serious effort will have to be made to explain to people the benefits of enlargement. We are talking about an enlarged market with enormous opportunities for indigenous firms as well as multinationals based here."
Mr Michael Buckley, group chief executive of AIB, also warned that the outcome, if it was allowed to stand, would do great damage to Ireland's economic future. "The fundamentals of the treaty should be re presented to the Irish public and the issues more comprehensively explained. A No vote will lose Ireland great goodwill among our existing partner countries in the EU, who won't understand why we voted this."
There was "no point in just bemoaning the outcome of the vote", he said. "We must find out why so many people did not recognise that it is so strongly in our national interest to vote and to vote Yes. I hope the Government, supported by Irish business, can find a basis on which it can represent the issues in a new referendum as soon as possible."
London market analyst Mr Michael Saunders, of Schroder Solomon Smith Barney, said the vote would probably be a negative for both the euro and the euro zone bond market, although the treaty did not directly influence monetary policy of the European Central Bank.
The vote had "symbolic importance" as an indicator of the extent of popular support for greater cohesion and co-operation among EU countries. The No vote highlighted small countries' concern about the dilution of their power in a broader EU, which had already threatened to derail the treaty at last December's summit.
The Irish rejection also raised the risk that EU countries would "squabble" over rewriting the Nice Treaty and institutional issues, rather than focus on supply side measures, he said.
In common with other observers, he noted that the Commission's criticism of Ireland's fiscal loosening probably did not help. "The vote is also likely to reduce the effectiveness of mutual fiscal surveillance among member-states, and increase the risk that countries take a loose fiscal stance."