The completion date for Dublin's Underground DART link estimated to cost €2bn has been put back three years to 2018.
However, the Government says the €2bn project remains a priority.
An Iarnród Éireann spokeswoman said that the planning applications had taken longer than expected and the project along with others in Transport 21 had been 'elongated'.
Iarnród Éireann today issued a video presentation and is also holding a series of public consultations before next month's application for a railway order to An Bord Pleanála.
Transport Minister Noel Dempsey previously described the 7.6km underground rail link as the most critical piece of public transport in the State.
However, today Minister Dempsey said that he had not been told about the delay.
Mr Dempsey said if the company is making such a decision, they will be hearing from him. He said he was not aware of any change and that he would be seeking clarification immediately.
The project will be a public-private partnership and part-funded by an European Commission agency.
It will link the Docklands with Heuston Station and Inchicore through underground stations at Pearse Street, St Stephen's Green and Christchurch.
It will also provide an interchange with all local and national rail services, including the Luas and planned Metro lines.
The present coastal DART line will be split with the Northern line going underground at the Docklands and the Southern line going through Connolly and onto Maynooth but the underground interconnector will provide a interchange between the two.
Iarnród Éireann said that the increased capacity will treble the number of rail passenger journeys to 100m annually.
Work is now expected to start in 2012 and take six years to complete.
