The second Nice Treaty referendum marks a "crossroads" for Ireland which ranks in importance with the vote on the Belfast Agreement, according to the Taoiseach, Mr Ahern.
He writes in today's Irish Times: "We made the right choice in ratifying that agreement. How our people decide on the Nice Treaty will also be a decisive turning-point for Ireland."
There had been only one previous occasion since he became Taoiseach when "we stood at such a crossroads where we needed to make the right choice for our country and our children".
Mr Ahern says it is vital in the next referendum that greater numbers come out and vote. He also defends the decision to stage a second referendum.
"We would not be asking the people to vote on this issue for a second time if it was not a matter of vital national interest. In asking the Irish people to vote a second time, I do so humbly and with the greatest of respect," he writes.
Mr Ahern says he is fearful that a second No vote could cost the State "new business, new jobs and new growth".
He rejects the charge that this is scaremongering. "Absolutely not. Just read the current edition of the Economist Intelligence Unit. Their assessment is clear. They say a No vote by Ireland will be interpreted abroad as a move away from Europe".
Meanwhile Mr Ahern was challenged yesterday on Nice by the Sinn Féin TD, Mr Caoimhghín Ó Caoláin, who said the Government had "defied democracy" in the wake of the last referendum.