Bertie Ahern's future as Taoiseach is in doubt following the ultimatum from Progressive Democrats leader and Tánaiste Michael McDowell that he must fully explain the 1994 £8,000 Manchester payment to him by businessmen.
If Mr Ahern does not come up with a satisfactory response in the Dáil on Tuesday - or before - the life of the Fianna Fáil/Progressive Democrats Government will be seriously under threat.
The Taoiseach, it is understood, revealed the existence of the Manchester money because he believed The Irish Times had information about it but was unable to publish the details.
Today, Irish Times editor Geraldine Kennedy and Public Affairs Correspondent Colm Keena will appear before a public hearing of the Mahon tribunal to answer questions on this newspaper's report of the payments received by Mr Ahern.
If the crisis worsens, Mr Ahern, who yesterday became the longest-serving Taoiseach since Eamon de Valera, may face pressure to quit as Taoiseach and leader of Fianna Fáil.
Meanwhile, some in the Progressive Democrats now privately fear the crisis has gone too far and that Mr McDowell may be forced to quit as Tánaiste and take the party out of office.
Last night, Mr Ahern's spokeswoman said he had "been fully open" in the Dáil about the Manchester event and he had "no problem" about answering further questions in the Dáil on Tuesday. The fact that Mr Ahern's explanation will not take place until then, though, offers him time to provide a solution acceptable to Mr McDowell that could defuse the crisis.
However, there is a danger that the hurdle set by Mr McDowell could leave Mr Ahern facing a Dáil humiliation that would destroy his political credibility, inside and outside Fianna Fáil.
The crisis dominated a meeting of last night's PD national executive in the party's headquarters in South Frederick Street, near Dáil Éireann, attended by Mr McDowell.
His decision to raise the political stakes yesterday afternoon followed his unhappiness after reading a transcript of an interview Mr Ahern gave in Cavan before noon.
Strongly defending his conduct, Mr Ahern said he paid his own travel to Manchester, attended the event in "a private capacity" and not as minister for finance, and had not asked for the money.
The money was given to him after he attended a dinner with 25 still unidentified businessmen and briefed them on the changes then happening in the Irish economy.
Mr Ahern and Mr McDowell spoke by telephone in the early afternoon, but before Mr McDowell had read the transcript of the interview, which he had missed because he was speaking in the Seanad.
Clearly concerned, Mr McDowell said at 4pm: "I have to say that there are very significant matters of concern which are not completely put at rest by the facts now in the public domain."
The Taoiseach must identify all the donors involved, explain what the money was for, and whether it was accepted as a political, or personal donation, the PD leader said.
Though concern mounted last night, senior Fianna Fáil Ministers clung to the hope that Mr Ahern can handle the crisis.
Asked if the Government's future was under threat, Mr McDowell said he did not "want to put it in those terms at all", but "accountability and credibility" had to be sustained.
Sharply critical of Mr Ahern, Fine Gael leader Enda Kenny said he had never heard of a serving minister accepting fees for speaking at an event, either in public or private, in his 30 years in the Dáil.
"I tell you one thing, my standard would be very different. Were I in receipt of that payment for a speaking engagement I would be gone by now because the Fine Gael party would not stand for it," he said.
Labour Party leader Pat Rabbitte said Mr Ahern could not "pretend that meetings like that are in a private capacity. It is a breach of the ministerial code of conduct".