Renzi came under intense fire in speeches from his predecessor as PD leader, Pier Luigi Bersani, and another former party head, ex-premier Massimo D'Alema.
The dissidents are alarmed at changes to Article 18 of the 1970 Workers Statute, which protects staff from unjust dismissal.
But Renzi's line prevailed, with 130 votes in favour, while the dissents split, with 20 voting against and 11 abstaining.
















