The National Roads Authority is reviewing its commitment to a key project on the main Dublin- Galway road, following a controversial rezoning of land by Galway county councillors.
The rezoning may push the cost of the long-awaited bypass for Loughrea up by 30 per cent, according to Senator Ulick Burke of Fine Gael.
He has described as "outrageous" the move by Fianna Fáil councillors on the local authority on Monday night.
Local councillors had agreed not to breach the route of the proposed bypass, which was to become the outer limit of the town boundary.
However, a Fianna Fáil motion to rezone an eight-acre strip of land from agricultural to industrial was approved on Monday night.
This has pushed up the value of the strip and adjoining land, and may increase the cost of the bypass from €19 million to about €24 million.
The National Roads Authority has confirmed that it is now reviewing the bypass project, which has been sought for over 20 years.
Senator Burke said that he intended to try and win support for a motion to rescind the decision, which he had described as "reckless" and "arrogant".
A spokesman for the NRA said it was taking the matter very seriously.