Environmental activist Vincent Salafia is to take a High Court case in a bid to block the planned route of the M3 motorway through the Tara Skryne valley.
Mr Salafia is meeting his legal advisers over the coming days to discuss the case, which will be centred on environmental and heritage legislation.
It is expected that the legal team will seek leave from the High Court this week to take judicial review proceedings against last month's decision by Minister for the Environment Dick Roche to issue directions allowing for archaeological excavations on a series of sites along the route.
A spokesman for the National Roads Authority (NRA) said it was hoped archaeological work would get under way at the sites over the coming few weeks, "in accordance with the directions of the Minister".
On Thursday, Mr Salafia's legal representatives wrote to the Minister, the NRA and Meath County Council warning against any work taking place at the sites.
"The purpose of this letter is to remind you and other agencies of the State of the vital interests which are at stake and to express the belief that you will not countenance any acts which will impact in any way on heritage artefacts prior to institution of these proceedings," it stated.
Activists had called on Mr Roche to issue directions ordering the full preservation of the sites, requiring the rerouting of the road away from the valley.
The director of the National Museum, Dr Pat Wallace, wrote a detailed letter to Mr Roche as part of the Minister's consultations. This advised the Minister to issue a preservation order for the whole area around Tara.
Mr Roche has said his issuing of any orders would have been an interference with the already-concluded planning process.