Minister for the Environment Dick Roche is expected to formally announce his decision today on how the archaeological sites along the proposed M3 motorway through the Tara-Skryne valley, should be dealt with.
Campaigners had asked the minister to issue directions requiring the sites to be preserved in situ, which would require the re-routing of the road.
Last month Mr Roche, however, indicated that any decisions he made would not overturn the planning process which approved the route.
He will also announce directions relating to a major Viking site at Woodstown, which is to be preserved in situ, and will require the rerouting of the proposed Waterford bypass.
The decision on the M3 is expected to be challenged almost immediately in the High Court by groups campaigning for a route change.
Mr Roche has already indicated he would be issuing directions to allow excavations take place on more than 30 sites along the proposed route through Co Meath.
Last month he told The Irish Times the route had already been approved by An Bord Pleanála. "I am where I am," he said. "This has gone through the planning process." The excavations along the route are needed if the route is to proceed as planned.
If he had directed that the sites be preserved untouched in situ, the route would have had to avoid the sites.
Mr Roche is also expected to address the concerns raised by the director of the National Museum, Dr Pat Wallace, about the current route.
There was speculation last night he may make specific directions relating to protecting aspects of some of the sites, in order to address some of Dr Wallace's concerns.
In an 18-page letter Dr Wallace, who was part of a formal consultation process, outlined his opposition to the route, in particular a major interchange close to the Hill of Tara.
Mr Roche will also formally announce his decision ordering the preservation of a major Viking site outside Waterford which was discovered during excavations for the Waterford bypass two years ago.