Ronaldo, who spent nine years at the Bernabeu after joining from Manchester United, completed his switch to Juventus few days ago on a four-year deal.
Auto behemoth Fiat are based in Juve´s home city Turin and both are co-owned by the Agnelli family. The union added: "The owners should invest in vehicle models that guarantee the future of thousands of people rather than enriching only one", the union said.
Speaking to calciomercato.it, former Juventus and Italy defender Alessio Tacchinardi analyses what may be the effect of the arrival of Cristiano Ronaldo at Juventus on the Serie A.
Juventus would need to sell before they can add to their squad following suggestions that they are looking to offload one of their strikers to fund Ronaldo's move.
However, critic analysis reveals that Cristiano's exit from Real has not come out all bad for the Champions League winners. That means more sponsors, more TV money and more prize money, " he told the BBC.
"Today Real Madrid want to give thanks to a player who has demonstrated he is the best in the world and who marked one of the most brilliant periods in the history of our club and world football", Real Madrid said in a statement.
A Fiat Chrysler Automobiles union in the south of the country called for a strike to protest the purchase of the star player by Juventus Football Club, which, like the carmaker, is owned by the Agnelli family.
Some workers a Fiat Chrysler plant in Italy have registered their displeasure with the amount of money spent to sign the five-time Ballon d'Or victor.
Its members will walk out at 22:00 local time on Sunday and remain on strike until 18:00 on the following Tuesday.