Bruno Mars' first collaborator, "Nothin' On You" rapper B.o.B., owes several stacks -- to the tune of $3 million dollars -- to his former managers ... at least according to a new lawsuit.
In the legal docs, obtained by TMZ Hip Hop, Round Hill Music and Artists Rights Management claims B.o.B. violated a deal it struck in January 2017 which requires the rapper to hand over certain royalties associated with public performances of his tunes.
B.o.B's touring company is also named in the suit and he has 20 days to respond ... otherwise, it could become a very expensive legal default.
B.o.B tells TMZ Hip Hop, "I have not seen the lawsuit but am aware my former manager had entered into agreements without my knowledge. I take my business seriously and look forward to getting to the truth of what happened."
Independent business has been B.o.B's game as of late. His last album, 2021's "Murd & Mercy," was released on his own label.