Irish PM Bertie Ahern is facing renewed pressure after revealing that he accepted £8,000 (11,800 euros; $15,000) for a speaking engagement in 1994.
Bertie Ahern insists he broke no rules in accepting money
The Progressive Democrats, partners in Mr Ahern's coalition, have spoken of "very significant matters of concern".
Mr Ahern said earlier this week he received thousands of dollars in loans from friends when finance minister but that he had "broken no codes".
An opposition leader said Mr Ahern's position could soon become untenable.
The Irish Republic's parliament is due to debate the issue next Tuesday.
A general election is due in the first half of 2007.
'No official script'
The latest concerns over Mr Ahern's finances relate to a speaking engagement in Manchester in 1994, during his tenure as finance minister.
Mr Ahern said he received unsolicited money totalling £8,000 from about 25 businessmen after finishing a speech.
He was giving the speech in a personal capacity, he said.
"So, no official script, not an official function, not in my capacity as minister, paid my own way, spoke at the function and on one occasion the assembled group of about 25, plus the group who were with me from Ireland, gave me the sum of money that I mentioned."
But the disclosure prompted several politicians to criticise the prime minister.
Deputy PM Michael McDowell, leader of the Progressive Democrats, the junior partner in government, said: "Public confidence and the sustainability of government requires that these issues be addressed."
Enda Kenny, leader of the main opposition party, Fine Gael, called for a clear resolution of the ongoing controversy of Mr Ahern's finances.
"If these matters are not cleared up and continue to unravel, then the position of the Taoiseach will become untenable," he said.
Mr Ahern won support from the current finance minister, Brian Cowen, who said there was "no question" of anything dishonest or corrupt.
"Where is there any evidence to suggest that he compromised the performance of his public duties?" he asked.
Speaking on Irish television this week, Mr Ahern confirmed he received an IR£22,500 (28,000 euros; $36,000; £19,000) loan from eight friends in December 1993 and a further loan of IR£16,500 in 1994 from four others.
He said the money was to pay costs during his marital separation.