Nia Long is “quietly fighting” Lionsgate over a pay discrepancy for her role in “Michael” … at least according to a new report.

According to Puck News, the actress had a “favored nations” clause in her contract that ensured she’d make as much as her costars … but she reportedly learned Colman Domingo and Miles Teller had higher payouts than she did.

So, Nia’s reportedly “threatening to take the studio to mediation” for allegedly shorting her salary.

Nia’s character — Michael Jackson‘s mom, Katherine — doesn’t get a ton of screen time in the blockbuster biopic.

But Puck News reportedly read the original script … which showed Nia had a bigger part in the third act that allegedly included “a key scene at the end of the film.”