The studio, which holds the rights to the original film, has taken action against 91-year-old former boxer Jake LaMotta and the sequel's producers in a bid to block its release.
MGM claims it should have been offered first refusal on the screen rights to LaMotta's 1986 follow-up book, and that the new film's association with the Martin Scorsese original will tarnish its legacy, Deadline reports.
Newcomer Mojean Aria will play a young LaMotta in Raging Bull 2, with William Forsythe portraying the present-day incarnation. Joe Mantegna, Tom Sizemore and Penelope Ann Miller will also star in the film.
Scorsese and Robert De Niro, who starred in the original film, are not affiliated with the new project.
Raging Bull 2 is currently shooting in Los Angeles and is expected for release next year.
Watch a trailer for the original Raging Bull below: