Five social housing regeneration projects around Dublin city look likely to be delayed or even scrapped.
This follows confirmation from Dublin City Council that a developer involved in the public private partnerships had pulled out.
The construction firm, Michael McNamara and Company, said recent changes to building regulations, and the tough residential housing market, had made the projects unviable.
Opposition parties have called on the Government to step in.
Five projects are affected, including a €265m regeneration project at St Michael's Estate in Inchicore that had been planned for seven years.
Fine Gael described the collapse of the deal as a blow to the most vulnerable in Dublin society and called on Dublin City Council and the Government to take immediate action.
The Labour Party has also called on Dublin City Council to make alternative arrangements for the construction of 138 units at St Michael's which already have planning permission.
