"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.
"Cristiano Ronaldo has chosen Juventus and that is something special for Italian football", said Ferrera, who made 358 appearances for Juventus before managing the club between 2009-2010. "The owners should invest in auto models that guarantee the future of thousands of people rather than enriching only one".
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.
Milinkovic-Savic has developed a reputation as one of the most exciting young players in Europe since joining Lazio from Genk three years ago and he provided 14 goals and 9 assists last season as they narrowly missed out on Champions League qualification with a fifth-placed finish in Serie A.
The workers plan to strike at the plant in Melfi, Italy, between Sunday and Tuesday, according to Bloomberg.
In addition to controlling Ferrari NV and Fiat Chrysler through a holding company, the Agnelli family owns a majority stake in the Turin-based soccer club, and the union representing the players said the money should have been reinvested into the cars, Bloomberg reported.
The France global has starred at the World Cup in Russian Federation but was heavily criticised for his performance last term and has struggled to flourish in Mourinho's defensive system.
While football fans in Italy are celebrating the arrival of Cristiano Ronaldo, the workers of the Fiat Chrysler plant have gone on a strike.