In Arum's suit he claims that Al Haymon, who is a promoter for Floyd Mayweather Jnr. and controls Premier Boxing Champions, has stopped Top Rank from leasing venues for fights, which in turn stops Top Rank from doing fights with its own fighters and has limited their access to the television market.
On May 6, De La Hoya's Golden Boy Promotions filed suit against Al Haymon and his PBC financial backer, Wadell and Reed, wanting $300-million in damages plus alleging that Haymon repeatedly violated antitrust laws and the Muhammad Ali Boxing Reform Act.
Wednesday's Top Rank suit by Arum is for $100-million and a ban on future PBC cards.
In a statement released, De La Hoya applauded Arum for his stand in support of fighters.
"I applaud Bob Arum and Top Rank Boxing for stepping up on behalf of fighters not only in their own stable, but all across the sport," De La Hoya said.
"Those like Bob and myself who have spent the bulk of their lives around boxing understand that the Muhammad Ali Boxing Reform Act is a crucial piece of legislation that serves to protect boxers and enhance the sport.
"Golden Boy Promotions will continue to push forward with our own lawsuit to ensure our wonderful sport continues to grow in a competitive, just manner," he added.
Attorneys for Haymon responded to the lawsuit: "The lawsuit filed today by Bob Arum and Top Rank is entirely without merit and is a cynical attempt by boxing's old guard to use the courts to undermine the accessibility, credibility and exposure of boxing that the sport so desperately needs," a spokesman for the firm Kramer Levin Naftalis and Frankel LLP wrote, according the Los Angeles Times.