Members of the Building and Allied Trade Union, which represents construction workers, are refusing to leave their offices in north Dublin over a dispute with the union's top management.
The staff involved, who are also members of the Unite trade union, say they will continue to occupy BATU's head office at Blessington Street until their demands are met.
They say they have no confidence in the present leadership, and are demanding the resignation of the head of the union, and that the union opens its books to an auditor.
One of the occupiers of the BATU office said that there are about 10 or 11 members occupying the offices at any one time. Daniel O'Connell said that they have organised a roster, which will see a fresh team arrive each evening.
The members envisage the stand-off continuing for the foreseeable future.
The occupation follows a row with the union leadership, which began in May when two union employees - who are also members of the Unite trade union - were laid off.
BATU chief Paddy O'Shaughnessy said that there is 'no question' of him resigning, and noted that auditors had signed off on the union's accounts for 2007.
