The Taoiseach has welcomed the bishops' statement calling for a Yes vote in the Nice Treaty referendum, saying he believed there was "a moral issue" involved.
Mr Ahern said the Pope had made a number of strong statements, one of which was made in the Polish parliament, in favour of enlargement.
The Pope had made it clear that he believed there was an obligation on people to support the enlargement process.
"I don't think it is only a political issue, I think it is an issue that affects many things, including morality," Mr Ahern said.
The treaty was about enlargement and not about other things put out by people "trying to give disinformation".
He said those opposed to the treaty were saying to people that they should vote No if they were confused, but he didn't believe the public was confused.
Mr Ahern said the treaty was "about giving an opportunity to people subjected to the tyranny of Soviet rule for years" and giving them a chance to play a part in a democratic Europe.
"It is also about our sincerity to give them that opportunity," he said, and not about "the weather, the sun, the moon or the stars or all the other nonsense we have heard from a small minority."
He said Fianna Fail would not start its campaign in the Tipperary South by-election until after the referendum.
Mr Ahern was in Carndonagh on the Inishowen peninsula to open a holiday home for people with learning disabilities. Milltown House is the only facility of its kind in the State and includes a swimming pool, riding stables and activity room.
Socialist Party TD Joe Higgins last night described the statement by the bishops as "perhaps the most direct intervention by them in political life since the Mother and Child debate on an issue outside of divorce and abortion.
"It is extraordinary that the statement comes so late in the day. I challenge the bishops to debate with myself and others on the crucial issues and especially on the issue of the steps towards the militarisation of the EU. I challenge them to throw their churches open to the debate this Sunday so their members who disagree with their line can have equal say," he said.