The Minister for the Environment, Mr Roche, has been served with a solicitors' letter asking him to halt all works on the route of the M3 motorway past the Hill of Tara until he has made a decision on its archaeological impact.
The letter, which was sent on behalf of Mr Vincent Salafia, spokesman for the main group opposing the selected route, warns a court injunction will be sought to stop the works if the Minister does not do so himself.
However, the Taoiseach, Mr Ahern, yesterday threw his full weight behind plans to build the motorway.
"We have just gone through the planning process. An Bord Pleanála had the longest hearing in the history of the country. Somebody has to stop sometime and start building. We are trying to develop the country, trying to keep our people in the country, trying to get from A to B.
"I am not trying to upset the kings (of Tara)...If I had known that they were there I would have gone around them," he said, to cheers from party supporters in Navan yesterday.
"We were told that we needed far more archaeologists, so we hired more archaeologists, who are the fastest growing profession in the country, it seems to me."
Fianna Fáil's by-election candidate, Mr Shane Cassells, said "serial whingers" were stopping the construction of the motorway. "I will not tolerate people moving camp from Carrickmines (on the M50 route in Dublin)...I resent their intrusion into my area, but they will not stand in the way of progress."
It is up to the Minister to decide on the nature and extent of the excavations. If he declines to do so, an alternative route would have to be found for the motorway.
"The only way to lawfully protect the national monument at the Tara-Skryne Valley complex is to avoid that valley and to divert a portion of the motorway in an easterly direction," the letter from Hughes and Liddy Solicitors says. Copies of the letter are also being served on the National Roads Authority (NRA) and Meath County Council.