MEP Nessa Childers has said she felt it would have been "morally corrupt" of her to stay in the Parliamentary Labour Party.
She announced her decision to resign from the Parliamentary Party today, saying she felt shame at the policies Labour has been implementing in government.
She will now join fellow dissenters such as Roisín Shorthall, Colum Keaveney, Tommy Broughan and Patrick Nulty.
The Ireland East MEP said the Labour Party has lost its way.
She said: "I didn't agree to the party going into Government, I wouldn't have thought that was the right thing to do. This isn't just about saving the Labour Party."