The Sinn Fein Ardchomhairle has authorised the party to take legal action to overturn Mr David Trimble's ban preventing its ministers taking part in North-South Ministerial Council meetings.
The Sinn Fein leader, Mr Gerry Adams, stressed that the decision to go to the courts had been taken "in principle" and nothing would happen until the party had talks on the matter with the Northern Secretary, Mr Peter Mandelson.
Mr Adams said Mr Mandelson had the power to compel First Minister Mr Trimble to nominate and uphold the institutions. "I intend to talk to Mr Mandelson about that".
He said the onus in the first instance was on the two governments to protect and defend the agreement.
Speaking after a meeting with the Taoiseach, Mr Ahern, in Dublin, Mr Adams said Mr Trimble had succeeded in puncturing all of the political institutions, as all the strands were interlocked and interdependent. "This is of grave concern at this time."
"We are only in this bind because of the way the whole process has been led hostage to meetings every three months by the Ulster Unionist Council and I don't think anybody can do business on this basis.
"The current position is not sustainable in the long term. We are in a crisis and it needs to be resolved. The best way is for the British government to use its power in this situation under the Act and under the Good Friday agreement," Mr Adams said.
Asked if there had been progress on the policing issue, Mr Adams said "no". He said what the IRA did last week "was a very big thing for them to do".
"If the IRA is prepared to be courageous enough to do that, how can Mr Trimble put up the demands he has put up?" he added.