The European Commission has issued a final warning to the National Roads Authority concerning the building of the M3 motorway in Meath.
The letter dated in June says that the ongoing demolition of the Lismullen monument near the Hill of Tara is illegal, and that Ireland will face legal action this autumn.
The roads authority is continuing to record and destroy monuments in the path of the road, mostly recently a site at Baronstown which was demolished in the middle of the night last week.
Independent MEP Kathy Sinnott says road works must be stopped in the area at least until the Commission comes back after the summer.
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