Kanye, Diddy, Rick Ross -- Kings Of Rap Ripped Me Off ... Claims Artist

Atlanta rapper 9gotti's got himself some brass ones -- firing off a legal threat to 3 powerful rap icons -- Kanye West, Diddy and Rick Ross -- warning them to quit jacking his music.

At issue ... a French Montana track called "Gucci Mane" -- which Kanye helped produce. Chinga Chang Records claims the song belonged to 9gotti ... before Yeezus and the others stole it from him.

The record label sent a cease and desist letter that's pretty comical ... saying the ripoff may have been a "drunken oversight." It also takes a shot at Diddy -- accusing him of being a music thief -- and says Rick Ross should know better because he's an ex-correctional officer.

According to the letter ... French's song and 9gotti's tune are nearly identical. French's version hasn't been released yet ... and Chinga Chang is dead-set on making sure it never comes out.