The Green Party has called for work on the M3 motorway in Meath to be halted following the recent discovery of a prehistoric circular "henge" at Lismullen.
The party's environment and heritage spokesman Ciaran Cuffe said the discovery of the site proved the unsuitability of the proposed route and he called for all work to come to an end, in particular the massive floodlit Blundelstown interchange.
Work on the project was halted two weeks ago after the large enclosure - which is believed to date from the Iron or Bronze age - was uncovered some 2km from the Hill of Tara.
The director of the National Museum, Dr Pat Wallace, has urged the Minister for the Environment Dick Roche to order a complete archaeological excavation of the site.
Mr Roche is considering a report from Dr Wallace after the National Monuments Service inspected the Lismullen site.
Mr Cuffe said the Green Party supported the upgrading of the existing N3 Road and the restoration of the Dublin to Navan rail line.