Nineteen crew members on a Greek ship who have not been paid for six months have prevented the ship from sailing until they receive their outstanding wages.
The crew aboard MT Olympic Pride- a Panamanian registered tanker - stopped the vessel leaving Foynes in Co Limerick.
It is understood the ship's captain offered a lump sum to the mainly Eastern European crew but that this was rejected.
Mr Tony Ayton, Ireland's International Transport Federation representative, said: "The exploitation of the crew on such a scale, on the part of the Greek owners, is reprehensible".