The Taoiseach is expected to face fierce criticism when the Dáil resumes tomorrow over his appointment of Ray Burke.
Mr Ahern named Mr Burke to ministerial office in 1997 despite the rumours of corruption surrounding the TD.
Burke was yesterday sentenced to six months in prison yesterday after pleading guilty to failing to make tax returns on over £100,000 over a ten-year period between 1982 and 1991. Judge Desmond Hogan at Dublin Circuit Criminal Court said Burke had "abused his position".
Burke - who held the foreign affairs, industry and commerce, communications, energy and environment portfolios - was named minister for justice in Mr Ahern's cabinet in 1997 before being forced to resign in a passports-for-cash scandal.
Mr Ahern famously referred to the jailed former minister as "an honourable man" who had been "hounded" out of office. The Taoiseach also denied having any knowledge of impropriety by Burke, saying he had "been just about up every tree in north County Dublin" and found no proof to support the allegations against him.
The Fine Gael leader, Mr Enda Kenny, today said Burke's appointment showed serious flaws in Mr Ahern's character judgment. He claimed the Taoiseach promoted the former Dublin North TD despite the fact that he had been warned by Fianna Fáil figures of rumours about Burke's involvement in planning corruption and possible consequences for the Government.
"A previous taoiseach said that Bertie Ahern was the most cunning of them all. In the sense of his knowing Ray Burke as a person and as a public figure, and knowing of the internal Fianna Fáil discussions about this, he made that appointment as was his right," Mr Kenny told RTÉ's Morning Ireland.
"But I think it calls into question the essence of character judgment which is not about due process but appointment to government and to cabinet in the first instance."
He demanded an explanation in the Dáil as to why the Taoiseach appointed Burke despite the cloud hanging over his head.
Labour's finance spokeswoman, Ms Joan Burton, has also called on the Taoiseach to apologise for supporting Burke. "The conviction and sentencing of Ray Burke will, I hope, mark a watershed in the battle against tax evasion and against illegality by those who hold public office," she said.
The Green party justice spokesman, Mr Ciaran Cuffe, said he hoped the sentence would give more power to the tribunals investigating corruption. "No politician should be seen to be above the law, and today's judgment is a significant step forward," he said.
"This is the tip of the iceberg, and we hope that the ongoing work of the tribunals will shed more light on the murky world of Irish politics over the last 30 years."
But last night a number of Fianna Fáil TDs defended their party leader. Longford-Roscommon TD Mr Michael Finneran said Mr Ahern had been deceived by Burke, who had not been "up front" with him. "The leader can't be a detective," he said.
Laois-Offaly TD Mr Seán Fleming insisted it "would have been impossible" for the Taoiseach to have had "any prior knowledge" of impropriety by Burke.
A Labour party councillor for Dublin's North Inner City this morning criticised the fact that Burke was not handcuffed when being brought to prison after sentencing yesterday.
Mr Aodhan O'Riordain said Burke was "proved to be a thief and a crook" and should have been treated as one. "Justice must be seen to be done and treatment must be seen to be equal," Mr O'Riordain said.
"The handcuffing of Ray Burke would have gone a long way to convincing people that I represent that the system is blind to social background. This opportunity has been lost."
