The Minister for Justice, Mr McDowell, has accused anti-Nice campaigners of adopting contradictory, extreme positions on immigration.
He said Ms Patricia McKenna's call for uncontrolled immigration represented the opposite extreme to fears expressed by other No campaigners that EU enlargement would produce a wave of immigration into Ireland.
"The No campaign in Ireland is now spread between two opposite poles.
"Patricia McKenna believes in uncontrolled access to Ireland for all immigrants. The extremism in Anthony Coughlan's and Justin Barrett's joint position is that they are claiming that Ireland has rendered itself defenceless against immigration," he said.
The Minister pointed out that similar fears of mass migration were expressed in some member-states before Spain and Portugal joined the EU, but such fears had proved groundless.
The Government retained the right to protect the Irish labour market and the social welfare system from any distortion an unexpected wave of immigration might cause.
Mr McDowell was speaking in Luxembourg, where he is attending a meeting of EU justice and home affairs ministers.
Today they will discuss proposals to set common standards for the reception of asylum-seekers and other measures aimed at harmonising asylum and immigration policies.
Mr McDowell expressed caution about the proposals, insisting that the Government was determined to ensure that any changes in asylum policy would make abuse of the system more difficult.
The Minister will shortly present to the Government proposals to tighten up Ireland's asylum system that will include a controversial list of safe countries of origin.
Asylum-seekers from countries deemed safe would face a "fast-track" procedure and would almost always be rejected immediately.
Human rights campaigners elsewhere in Europe have long opposed such lists on the grounds that minority groups often face persecution in states that might otherwise be considered safe.
Mr McDowell promised that, if he decides to introduce a list of safe countries, he will provide a "safety valve" to ensure that people who need asylum will not be sent home.
The Minister for Agriculture warned that a second rejection of Nice could damage the interests of Irish farmers in Europe.
Mr Walsh, who was in Luxembourg for a meeting of EU agriculture ministers, said that a No vote could affect the outcome of negotiations over reforming the Common Agricultural Policy (CAP).
He cited a recent increase in EU subsidies for Irish beef exports to Egypt as an example of the importance of the good will of Ireland's EU partners.
He said that a No vote on Saturday would dent that good will and sap sympathy for Irish concerns.
The Minister predicted that, despite misgivings over CAP reform and discontent over domestic issues, farmers would back the Nice Treaty in Saturday's referendum.
"There's a far greater realisation of the importance of Europe to the agricultural industry. We're enormously dependent on the European market," he said.
