The challenge, which will seek an injunction against all preparatory work on the area, is currently being prepared and will be lodged before 31 January. The challenge is to be taken by members of the Campaign to Save Tara and will argue that sites uncovered during preparatory work on the area should be classified as national monuments.

A previous legal challenge to the route failed in the High Court, although it did manage to delay work from being carried out on the site. The new challenge is believed to focus on a separate aspect of the existing legislation.

Campaigners last week halted tree-felling work from being carried out along the planned route. A group of protesters halted lorries and diggers from carrying out tree-felling work close to Rath Lugh. According to a spokesman for the group, they plan to continue their protests at the site over the coming weeks.

Since preparatory work began, a total of 38 previously unknown sites of archaeological interest have been discovered. While the National Roads Authority (NRA) denies that any of these sites is significant enough to be labelled as a national monument, the basis of the forthcoming legal challenge will centre around claims that, under existing legislation, work on a site must be halted if new sites of national interest are discovered.

A spokesman for the Campaign to Save Tara said that the group was not against the construction of a much-needed motorway linking Meath and Dublin, but was opposed to the route chosen for the road. By cutting through the TaraSkryne Valley, the motorway was destroying the richest area of archaeological heritage in Ireland, he said.

The Director of the National Museum of Ireland , Dr Pat Wallace, has previously been strongly critical of the route of the motorway, as have several international archaeological experts.