Tupac Shakur had a promiscuous reputation in the early 1990s … and a much-anticipated new book claims it drove Janet Jackson to ask the studio to have him tested for AIDS before a kissing scene.

Jeff Pearlman — a noted biographer — has written a new book titled “Only God Can Judge Me: The Many Lives of Tupac Shakur” … and, in it, he touches on Tupac’s time filming the 1993 flick “Poetic Justice” with Janet.

According to Pearlman, the two didn’t get along much … with Janet a consummate professional on-set while Tupac had a tendency to come and go as he pleased.

Days before a kissing scene between Pac and Janet, Pearlman writes, Tupac apparently kept talking about “overwhelming Jackson with his lips and mouth” … and, ultimately, Steve Nicolaides — a producer on the movie — was called to her trailer.

Nicolaides tells Pearlman Janet — sitting with her then-fiancé René Elizondo Jr. — expressed concern about Tupac’s playboy persona … and he says she told him she didn’t “want to swap saliva with him until I’m really sure that he’s healthy and clean.”

Steve dutifully went to Pac with the request … who apparently responded with a NSFW tirade aimed at Jackson before flat-out refusing to take the test.

Nicolaides says he doesn’t blame Janet for asking about the test … AIDS was still running rampant in the early 1990s — and, he admits Pac had garnered a rep, so it wasn’t the most unreasonable request.

The movie still did pretty well despite the tension … making $27 million at the box office against a budget about half that size — and, it’s still a fan-favorite to this day.