The State would be in breach of European legislation if it was to grant permission for the Luas line linking St Stephens Green and Broombridge, a planning hearing has been told.
Peter Sweetman, who is objecting to the proposed Luas line via Dawson Street and O'Connell Street, told a Bord Pleanála hearing that the European Court of Justice had found Irish legislation in relation to Environmental Impact Assessments was flawed.
"This hearing in not taking into account recent European Court decisions is acting illegality, the court clearly found Irish legislation on what constitutes an assessment was insufficient" Mr Sweetman said.
Mr Sweetman later told The Irish Times his argument was that environmental impact "statements" that were accepted under Irish legislation were not sufficient to meet the requirement for an environmental "assessment" under European legislation.
The Railway Procurement Agency is seeking permission from Bord Pleanála for the line, which would provide a city centre link between the existing Luas Red and Green lines, as well as extending the tram network to Broombridge in the north city.
Dublin City Council has already called for power cables for the line to be buried in the ground as opposed to hanging from adjacent buildings. However the agency has said there are a number of difficulties with underground lines.
The agency has submitted photographs of similar lines in France, which utilise underground power supplies, where snow falls have caused the network to close.
The agency also produced photographs of snowfalls in Dublin last December in which the Luas trams were able to keep moving, a factor the agency attributed to overhead power cables.