Quentin Tarantino Allegedly Threatened Brad Pitt During 'Once Upon a Time in Hollywood'

Quentin Tarantino and Brad Pitt made a classic with "Once Upon a Time in Hollywood" ... but it seems there was a super intense moment between the two men while shooting the 2019 flick.

'Hollywood' costar Bruce Dern explained that during one of his scenes with Pitt, QT got so pissed at the superstar actor ... he threatened his career.

Basically, Dern says he improvised a line, and a surprised Brad called "cut" ... and that really sent Quentin over the edge, the writer-director allegedly telling him ... "Never again in your life will you ever cut a camera, or you'll be dead in this business. That's my domain. Don't stop behavior."

A source close to Brad told TMZ ... if this story is even true, the duo are pals who have done amazing work together. And once upon a time in Hollywood ... no one would have even cared about this alleged moment.

From what Dern told PEOPLE ... they got through the scene fine afterwards -- and the movie was a huge success at the box office and scored Brad an Oscar for best supporting actor.