Dun Laoghaire-Rathdown County Council was warned last night that its "rezoning policies" would erode the last green belt between Dublin and Wicklow.
The warning came as Fianna Fail councillor Mr Larry Butler successfully proposed that a 22-acre site at Ballyman Road, Bray, be rezoned for housing.
Outlining his opposition to the proposal, Mr Denis O'Callaghan (Democratic Left) said it "would sound the death knell of the green belt between Shankill and Bray."
Arguing that, while the proposal was for just nine houses, it would be a precedent for further development of the area, Mr O'Callaghan added, "Make no mistake about it, this is the green belt and it is sacrosanct."
Mr O'Callaghan also rejected suggestions that the purpose of the rezoning was to provide homes for a farmer's adult children.
The members voted by a majority of two to rezone the site.