Labour leader Eamon Gilmore says alleged contradictions surrounding the Taoiseach's evidence to the Mahon Tribunal threaten to undermine his credibility.
Mr Gilmore today described the testimony Bertie Ahern gave to the tribunal in September as "confused, contradictory and scarcely believable".
He says Mr Ahern will not be able to survive unscathed if he repeats this performance when he returns to the tribunal before Christmas.
The Labour leader also says speculation about Mr Ahern's future will paralyse the Government as ministers jockey to be in a prime position if he resigns or is forced out of office.