Young people would be the main victims if the Nice Treaty was rejected again, Mr Peter Sutherland, the former European commissioner, has warned. "The real price of voting No would be paid by our young in the reduced opportunities that would follow," he said.
"Inward investment has been the one essential aspect of our economic progress. The figures are startling, particularly from the US, and about 70 per cent of our industrial exports are from US companies.
"Virtually none of these jobs would have been provided in the absence of our full participation in the European Union. Our domestic market is simply not large enough to stimulate large-scale investment.
"Industry everywhere will look on a negative vote here as being damaging to our standing in Europe and as raising serious questions as to our commitment to full participation in Europe."
Mr Sutherland, who is chairman of BP and former director of the World Trade Organisation, was a scheduled speaker at a Fine Gael meeting in Dublin.
Meanwhile, a new organisation called Equal in Europe has been launched in Dublin to campaign for a No vote. The group is composed of "citizens who are pro-EU, pro-enlargement and opposed to the Treaty of Nice".
A barrister and group spokesman, Mr Neil Patrick McCann, underlined the "potential damage" to Ireland if it lost the automatic right to nominate a member of the European Commission at such time as there were 27 EU member-states.
"The automatic right to a commissioner has always been seen as a counterbalance in circumstances where sovereignty was being pooled. The loss of the automatic right to a commissioner is utterly unnecessary and ultimately harmful to the EU as a whole," he said.
"Commissioners play an important role in representing the EU in their home countries, and their loss for potentially one-quarter of the time will lead to a sense of alienation on the part of ordinary citizens.
"It will only serve to increase suspicion and mistrust about decision-making in the EU.
"Furthermore, the Commission is the guardian of the interests of the Union as a whole, not just a representative of member-states. Its legitimacy as a guardian for these interests is subverted in circumstances where, at any one time, several countries may not be represented," Mr McCann said.
He rejected claims that a No vote would hit inward investment. "Ireland's status as a full member of the Union would remain intact in the event of the treaty being rejected. The economic arguments used to scare voters into accepting the treaty are just not relevant to this debate," he said.
A vote against Nice was not a vote against enlargement.
"If Nice is defeated, the enlargement process will continue. The difference is that the original model of partnership, unity and equality will have been preserved to the benefit of the smaller member-states, including the applicant nations," Mr McCann said.
Calling for a Yes vote on a visit to Dublin, the President of the European Parliament, Mr Pat Cox, said the referendum was a "defining moment" for Ireland.
"A further rejection of the treaty after such a long pause for reflection would signal a disconnection from Ireland's European adventure - the first unbundling in a generation of one of the indispensable foundations of modern Irish success," he said.
There was no basis for fears about migration from the accession states. "These tactics are familiar and have much in common with leaders of the far right in continental European politics."
Mr Cox was guest speaker at a lunch organised by the Association of European Journalists.