Hip-hop producer Dj Mustard is facing legal action from a childhood friend over royalties for a string of rap hits, including Tyga's catchy Rack City.

Mike Free claims he wrote, composed and recorded the music for an early cut of the 2011 track, but Mustard took full credit for the tune after it was picked up by Tyga.

The plaintiff alleges he was also the brains behind songs like I'm Different by 2Chainz, Don't Tell 'Em by singer Jeremih, Big Sean's I Don't F**k With You and Jamie Foxx's Party Ain't a Party, but failed to receive credit, and subsequently missed out on a big pay day.

Free is now suing DJ Mustard, real name Dijon MCFarlane, for his cut of profits and proper producing credit, according to Tmz.com.