Sinn Fein has said it will "forcefully" lobby the Taoiseach over Mr David Trimble's ban on the party's attending North-South Ministerial Council meetings.
The party is to meet Mr Ahern in Dublin today to discuss the sanction, which Mr Trimble applied in protest at the lack of movement on Provisional IRA decommissioning.
The party has already protested to the Northern Secretary, Dr John Reid. Mr Trimble's ban was declared unlawful by Belfast High Court but the First Minister plans to appeal.
In Belfast yesterday the Sinn Fein vice-president, Mr Pat Doherty, said: "David Trimble is acting unlawfully" and they would say that to Mr Ahern.