The governments of the EU member-states must not "push the boat out too far" on political integration at the Nice summit in December, the Fianna Fail MEP, Mr Gerard Collins, has warned.
Addressing the European Parliament in Strasbourg, Mr Collins said there could be difficulties in subsequent referendums on the treaty if the summit went too far along the path of integration.
He urged the various EU governments to "seriously reflect" on the result of the recent Danish referendum where membership of the common currency was rejected.
"This decision of the Danish people comes only a matter of two months before EU leaders are set to meet in Nice to reform existing EU treaties and EU policies," he said.
Mr Collins, who was speaking on behalf of the Union for Europe grouping in the parliament, said he supported EU enlargement which would "help build a European continent at peace with itself".
"However, EU member-state governments face difficult choices. We cannot deny for one moment that the Danish people used the recent referendum as a test of confidence in the structures of the European Union.
"Serious concern was expressed among Danish voters that the elimination of tax vetoes within the European Union would dissipate future social security benefits.
"I do not necessarily support this particular assertion. However, the point remains the same, namely, that the EU member-state governments, the European Commission and the European Parliament have a serious battle on to persuade the 370 million citizens of the EU that greater political and economic integration is the way forward for the European Union itself."