The new Minister for the Environment, John Gormley, has said legal advice from the Attorney General's office confirms that he has no authority to overturn the decision to allow the M3 motorway to be built over an archaeological site.
Opposition parties had claimed the Mr Gormley does have the power to over-turn the decision.
This morning, Mr Gormley said his initial view was he was not going to be able to do anything about his predecessor's decisions, despite his commitment to protecting heritage.
He said he will review the documentation and talk with the Director of the National Museum before giving his definitive announcement.
However, Labour's Eamon Gilmore has said Mr Gormley does have the power to revoke Mr Roche's order, under section 22 of the Interpretation Act 2005.
Fine Gael's Fergus O'Dowd charged that the reason Minister Gormley had not done it was because he was politically emasculated by his new Fianna Fáil masters.
It has been a tough first day at the office for the Green Party Chairman as this heritage row overshadows his new Ministerial position.
Just before clearing his desk, Mr Roche, the outgoing Minister, signed an order which allowed a National Monument near Tara to be studied and then destroyed to make way for the M3.
Mr Roche has defended his last-minute decision, saying he read the documentation, consulted widely and took the appropriate decision.
Minister Roche said it would have been a discourtesy to hand over a difficult decision as it amounted to passing the buck.
Mr Gormley said he was committed to protecting Ireland's heritage and would have an open door to like-minded people.
Green TD Ciarán Cuffe has said he was upset by Mr Roche's decision and expressed his hope that Mr Gormley can now reverse it.
Meath Archaeological and Historical Society spokeswoman, Julitta Clancy, said it may not be too late to change the contract to allow the re-routing of the motorway.
She added contracts should allow ministers this flexibility.
If the decision stands, work on the M3 at Lismullen will not resume for some time until the archaeological work is complete.
Work on other parts of the motorway will continue as normal.