The Labour leader said the latest controversy in the Sheedy case could have implications for the stability of the Government.
Mr Ruairi Quinn said the Tanaiste, Ms Harney, would have to make a judgment on whether information was withheld in an unacceptable manner. "It may well be that is another straw. As to whether it is the final straw, I do not know."
Speaking to journalists in Tralee, Mr Quinn said: "This is increasingly a Fianna Fail ring. There were representations made by a former Fianna Fail TD, Jim Tunney, and by a Fianna Fail TD, Brian Lenihan. There was a visit to the open prison by the former councillor, Joe Burke. The two judges prior to their elevation to the bench were known to be Fianna Fail supporters and activists, and there was nothing wrong with that.
"Looking at it from the outside, until we know otherwise, it seems to me to be a Fianna Fail ring in which the Taoiseach is involved."
Mr Quinn said Mr Ahern had an elaborate constituency office. "The idea that he would have no memory of the representation, or that his system would have no memory of it, is something I find somewhat difficult to credit."
The conference heard an emergency motion which deplored the failure of the Taoiseach and the Minister for Justice to reveal the representations Mr Ahern made in the Sheedy case.
The motion, passed unanimously, read: "Conference, mindful of the revelations in today's Sunday Tribune that the Taoiseach made direct representations to the Department of Justice on behalf of Mr Philip Sheedy four months before Mr Sheedy's early release from prison, deplores the failure of the Taoiseach to declare his actions in Dail Eireann, the failure of the Minister for Justice to inform the Dail and the public of the Taoiseach's involvement, and demands a full explanation from the Taoiseach concerning his involvement in, and knowledge of, this whole affair."
The party's deputy leader, Mr Brendan Howlin, said Mr Ahern was accountable to the State and to the Dail. "He had ample opportunities, some as late as last week when he answered questions in the Dail, to explain himself. He failed to do so."
Mr Pat Rabbitte (Dublin South West) said: "This act of a deceit is the work of a man who seems to have a lot to hide."