BRUNO MARS SUES MUSIC PUBLISHER

Bruno Mars  is declaring war on his music publisher  -- claiming the company refuses to let him out of his contract ... even though he has already delivered on his end of the bargain.

Mars has filed a lawsuit against Bug Music, Inc. -- claiming the company failed to pick up the option on his contract after he delivered an agreed upon number of songs.

In the documents, filed today in L.A. County Superior Court, Mars claims he turned in all of his music by  February -- at which point, Bug had a certain amount of time to exercise its option to continue the relationship with Mars.