An Bord Pleanála has blocked a €50m convention centre project planned by Mr Jim Mansfield for the Citywest Hotel complex near Saggart in Co Dublin.
An Bord Pleanála voted 7-1 to refuse permission following An Taisce's appeal against the scheme.
An enforcement notice was served on Mr Mansfield's company, HSS Ltd, last September - two months before the county council decided to grant permission - when it became clear that site development works were already under way.
A considerable amount of work was carried on the site and a large steel frame for the centre is already in place.