Gingrich has been using the Eye of the Tiger song from Rocky III as his campaign theme anthem since 2009. The lawsuit claiming copyright violation was filed by Frankie Sullivan for his Rude Music Inc., which owns the copyright.
The complaint filed in an Illinois federal court states that Gingrich and his campaign have used the song in their political rallies, without taking permission to do so.
Eye of the Tiger is a 1982 hit song from the Survivor Rock band's album of the same name. The song was later used in Sylvester Stallone's movie Rocky III.
Chicago-born Frankie Sullivan co-authored the Grammy award-winning song with fellow Survivor founding member Jim Peterik. However, Peterik is not party to the lawsuit and reportedly said that he didn't have a problem with Gingrich using it, according to a Sun Times report.
Watch the Gingrich campaign video that uses the tune here.