Rapper Ludacris is being sued by a Chicago rapper, who goes by the name of Marvo-- claiming the rapper stole several lyrics for his hit song "Sex Room."

In the docs, filed by Marvo, claims he's the real author of the single, and concocted the original concept for "Sex Room" back in 2009... a year before Luda released it with Trey Songz.

Marvo also claims he'd been working with a producer named Kajun--but the dude sold the song to Ludacris behind his back. Marvo says Ludacris changed parts of the song...but released it with many of the original lyrics, including multiple lines written by Marvo-- such as, "Welcome to my sex room" and "It's a private party."

TMZ reports, Marvo says he hasn't gotten a penny for his tune and is now suing Luda and Trey for an unspecified amount of money.

But we have to give credit where credit is due … there are a bunch of genius lyrics on “Sex Room” that Ludacris came up with himself … like, “Feelin’ high but I’m hung real low / Lookin’ sorta like a tripod.”

Ludacris have not yet responded to the allegations.