Voters must base their decision about the Nice Treaty on the question of EU enlargement, and not on domestic economic issues, the Taoiseach, Mr Ahern, has said.
Speaking in Donegal after the Cabinet agreed to hold the referendum on Saturday, October 19th - the first time a national political issue will be put to the people at a weekend - Mr Ahern said the referendum was about "the minor institutional arrangements" necessary to expand the EU to 500 million people.
He criticised as "highly irresponsible" yesterday's call by the Tipperary South Independent TD, Mr Seamus Healy, for voters to use the referendum to punish the Government.
"I would say to Seamus Healy: he obviously doesn't take his national responsibilities much into account and it is a pity that a public representative takes that view.
The EU population is set to grow to 500 million, said Mr Ahern. "The decision facing us is whether we want to be part of that, or do we not - or even worse still, do we want to block it, even though we would ultimately fail."
Welcoming the confirmation of the date, the President of the European Parliament, Mr Pat Cox, said October 19th would be a defining moment for Ireland and Europe.
The anti-Nice group, Equal in Europe, also welcomed the setting of the date and expressed the hope that "a real debate on the issues of concern to voters would commence immediately".
Mr Justin Barrett, of the No to Nice Campaign, accused the Government of "ramming through" the referendum in the minimum statutory period of 30 days. He welcomed that it would be held on a Saturday, claiming that young people were more likely to vote No.
The Government strongly rejected suggestions that it had delayed setting a date, or that it had deliberately chosen the shortest possible campaign.
Urging voters to "spend 20 minutes" reading the information booklet produced by the Department of Foreign Affairs, Mr Ahern said: "Then they will be very well informed."
The 30-day period is the minimum allowed by the Constitution, but European Union meetings and November's dark evenings meant it could not be held later.
The Tánaiste, Ms Harney, said the legislation necessary to hold the referendum had only passed the Oireachtas last Friday.
The Taoiseach and the Minister for the Environment, Mr Cullen, said they believed the move to Saturday voting would encourage younger voters, particularly those attending third-level institutions, to turn out and vote Yes.
Ministers have been told effectively to clear their diaries between now and October 19th, to back the Yes campaign.
The President of Poland, Mr Aleksander Kwasniewski, last night said that an Irish rejection of the Nice Treaty might not stop European Union enlargement, but it would make it much more complicated.
He told RTÉ News: "But you in Ireland have to have the sense of responsibility that this referendum goes beyond issues that are internal to Ireland, that it has an all-European dimension."
Polling stations will be open on October 19th from 9 a.m. to 9 p.m. for 2,923,918 registered voters. Applications from people wishing to be added to the supplementary voting register will be accepted until October 4th.
Meanwhile, the Department of Agriculture has denied that the payment of EU agricultural premiums has been brought forward to influence farmers to vote Yes.
The Department had sought the European Commission's approval to advance the payment of €510 million to help farmers cope with this year's appalling weather, said a spokesperson.
