* Hardline union opposes Fiat productivity deal
* Fiom set to call 8 hour strike on Jan 28
* Split in union movement
(Adds new labour deal at Fiat's Naples plant)
By Laura Viggiano
ROME, Dec 29 (Reuters) - The head of Italy's hardline metalworkers union Fiom called on Wednesday for an eight-hour strike on Jan. 28 to protest against productivity deals agreed by other unions at Fiat SpA's Italian plants.
Fiom, Italy's largest metal-workers' union and part of the left-wing CGIL confederation, has been at odds with other unions over a drive by Fiat Chief Executive Sergio Marchionne to introduce more flexible working practices.
Fiom chief Maurizio Landini described Fiat's plans as "an anti-union, anti-democratic, authoritarian initiative which is without precedent in our country".
Fiom's governing body will vote on Landini's proposal later on Wednesday, but is virtually certain to approve it.
The dispute over the future of Fiat's plants in Italy has highlighted the battle to reform industrial practices and reverse a steady slide in competitiveness that has blighted the euro zone's third-largest economy for years.
Marchionne's plans to increase the number of shifts and limit strikes and benefits, fiercely opposed by Fiom, have been accepted by smaller, more moderate unions.
Four such unions on Wednesday said they had signed an accord with Fiat over new working practices at its plant in Pomigliano, near Naples, replicating a deal already signed at its Mirafiori plant in Turin and further isolating Fiom.
Fiat has set up a new company in Pomigliano in order to avoid the terms of a national labour contract for metal workers signed by employers' association Confindustria.
Italian labour productivity has grown far less than that of most of its European partners in recent years and investment from abroad has languished, but Landini said Fiat was trying to erode basic workers' rights.
"They want people to accept the idea that we have to cancel contracts, cancel rights, and even cancel out free unions from the factories in order to have investments, but this is false," Landini said in a television interview.
However, with Italy's unions deeply and often acrimoniously divided, his call for all Italian metal workers to follow Fiom's lead is unlikely to be heeded.
Luigi Angeletti, leader of the moderate UIL union confederation, attacked Fiom and said the CGIL, Italy's largest confederation, was making itself irrelevant by refusing to negotiate with employers and the government.
"Fiom has been a political organisation for more than 10 years and it behaves as such even when it pretends to be a union," he told La Stampa daily. (Additional reporting by Giuseppe Fonte; Writing by Gavin Jones; Editing by Will Waterman and David Holmes)