Car maker Fiat SpA stopped short of sealing its near $1 billion investment for the survival of its Naples plant after less than full labor support for plans to boost productivity there.

Backing for Fiat CEO Sergio Marchionne's groundbreaking plan on working conditions -- seen as a watershed for Italian industrial relations -- came from around 62 percent of 4,642 workers who voted on Tuesday at the Pomigliano plant.

Marchionne had demanded unanimous support from five unions at the plant before investing 700 million euros ($939.2 million) and starting production of the new Panda model.

Fiat acknowledges the impossibility of reaching agreement with those obstructing ... the plan to relaunch Pomigliano, the company said in a statement.

The company will work with those unions who took up the responsibility of the accord to find and enact together ... conditions needed to realize future plans, it added.

The statement made no mention of the investments or car production and while some union members felt it was positive, there were calls for clarity.

It confirms the investment. The Panda will come to Pomigliano. I also think Fiat will want more guarantees, so there is work to do, said Bruno Vitali, head of one of the unions supporting the deal.

But Giuseppe Farina, a leading official in part of the same union, said he wanted more detail.

I am interested to understand if Fiat is confirming the Panda project at Pomigliano. If Fiat is not confirming that we are strongly against, he said.

Rocco Palombella, head of another union, said a Fiat proposal to set up a new company to employ those workers agreeing to the deal would not be acceptable.

It's an idea that Fiat put forward ... we said we didn't agree. It would be a problem, Palombella told Reuters.

An industrial analyst said Fiat could even be thinking of producing something other than the Panda at the plant.

The Panda -- now produced at Fiat's plant in Poland -- is an important model for the group and Marchionne does not want to risk moving production to Italy without cast-iron guarantees there will be no quality problems or failures in supplies.

He wants to make shifts at the Naples plant more flexible, restrict strikes and limit benefits such as sick days.

Labor Minister Maurizio Sacconi said Fiat should be satisfied with the unequivocal ballot result.

Four out of five unions at the plant expressed support for Fiat's proposal, with only the Fiom union saying the plan broke rules on rights to strike and sick leave. Fiom called on Fiat to reopen negotiations to reach consensus.

Fiat shares closed down 2 at 9.325 euros while the STOXX Europe 600 auto index .SXAP dipped 1 percent.

HIGHER PERCENTAGE

Fiat aims to boost employment at the plant to 15,000 and produce as many as 300,000 Pandas a year at Pomigliano. Two-thirds of the 8 billion euros to be invested under its 2010-2011 strategic plan have been earmarked for Italy.

Pomigliano, in Italy's underdeveloped and crime-plagued south, has a history of labor unrest and the worst productivity of all five of the company's domestic plants, even taking into account slow demand for its Alfa Romeo models. ID:LDE5BL1SA

With Italy's economy struggling to emerge from its worst post-war recession, unemployment in the region is already running far above the national average of nearly 9 percent.

Fiat is Italy's biggest manufacturer and a major player in its car industry, which accounts for 11.4 percent of the 1.5 trillion euro economy.

Economists say the proposed deal could set an important precedent for labor relations nationwide, moving Italy into line with more productive European nations such as Germany.

(Additional reporting by Laura Viggiano in Pomigliano, Stefano Rebaudo in Milan, Gianni Montani in Turin and Francesca Piscioneri in Rome; Editing by Charles Dick and Michael Shields)

($1 = 0.7453 euro)

Poland