Labor leader Amir Peretz says his election partner and Gesher leader Orly Levy will not back Blue & White chief Benny Gantz as prime minister.
Gesher, through its partnership with Labor, had been counted among the 55-strong center-left bloc backing Gantz as the best candidate to form the next government.
But even if Levy decamps to the right-wing bloc, which she has not announced, her one Knesset seat will not give Benjamin Netanyahu the 61 seats he needs to form a stable government.