In October Fiat Chrysler and Peugeot owner PSA unveiled plans to create a $50 billion group, set to become the he world's No.4 automaker.

But analysts fear the merger could create a group with spare production capacity of almost six million vehicles in a slowing autos market.

Fiat Chrysler has pledged to invest 750 million euros in its Mirafiori plant in Turin, as part of a 5 billion euro plan to 2021 for Italy, but FIOM said in a statement that a new business plan was necessary to increase production and boost jobs.

(Reporting by Giulio Piovaccari, editing by Valentina Za)