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.
The Agnelli family, which has owned Turin-based Juventus for more than 90 years, controls Ferrari and Fiat Chrysler through its holding company, Exor, which owns 64 per cent of Juventus.
For the USB union, the decision means Fiat is missing out on investment.
Tacchinardi began by hailing Ronaldo's arrival stating that: "He certainly gives a new image to our football".
"The property should invest in vehicle models that guarantee the future of thousands of people rather than enriching only one", the union said in a public statement. "The owners should invest in vehicle models that guarantee the future of thousands of people rather than enriching only one".
"It's maybe reductive [to say Juventus need Ronaldo to win in Europe], but if you think about the final between Juventus and Real Madrid, he scored twice", the former AC Milan defender told Goal. Cristiano can change Serie A to the point that, in the future, we will become accustomed to spending big money on star players to attract them to Italy.
To drum home their concerns, the USB union has called for a strike at the Melfi plant in southern Italy.
He has also built a legacy that will forever be remembered by the world.