The family of murdered solicitor Pat Finucane are to appeal to the Taoiseach to back their call for an open inquiry.
Geraldine Finucane and the murdered man's son Michael announced they would approach Mr Ahern following an angry meeting with Northern Secretary Peter Hain at Stormont yesterday at which the terms of an inquiry were discussed.
The British government has vowed to hold an inquiry into the 1989 murder, but under the new inquiries act, which could mean much of the inquiry would be in private.
The findings would also be subject to redaction by the government to protect British intelligence services.
The Finucanes have relentlessly campaigned for an independent, open and public inquiry. They claim that the new legislation would mean any inquiry would fall short of required standards of openness and independence.
Mr Michael Finucane said Mr Hain had consistently underlined his government's intention to hold the inquiry under the new inquiries act.
"It renders the panel devoid of independence and retains control with the government minister through use of restriction notices. Therefore we doubt its capacity to get at the truth," he said.
Mrs Finucane described the meeting as "frank, very frank", and suggested the Northern Secretary was inflexible and was placing the concerns of the intelligence services over the need for justice.
Judge Peter Cory, a retired member of the Canadian supreme court, investigated the case following political talks involving the British and Irish governments at Weston Park in 2001 and recommended an inquiry.
However, Judge Cory has since made it clear that he is opposed to the holding of an inquiry under new, tighter legislation.
"To change the ground rules at this late stage seems unfair," he said. The legislation, he added, would make a meaningful inquiry impossible.
"I cannot contemplate any self-respecting Canadian judge accepting an appointment to an inquiry constituted under the act."
A range of human rights organisations has backed the Finucanes, and Jane Winter of British-Irish Rights Watch accompanied the family at the Stormont meeting.
The Irish Government has publicly backed their call for an inquiry.
The Northern Ireland Office said after the meeting: "The government believes that an inquiry under the act would be the only really effective means of getting at the truth.
"The secretary of state undertook to reflect on the points Mrs Finucane made."
The Finucanes are to meet DUP leader the Rev Ian Paisley on Monday to discuss the case.