8/20/2010 12:25 AM PDT by TMZ Staff
Montana Fishburne claims she got screwed by her sex tape partner ... over footage of some eXXXtra-curricular work they did on the side -- and now she's hired some lawyers to clean up the mess.

TMZ has obtained several letters that Fishburne's legal team fired off to a porn star named Brian Pumper -- demanding that his production company immediately stop all sales of "Phattys Rhymes & Dimes 14" ... which features a scene between Montana


According to the letters, Montana never signed a release for Brian to use the X-rated material in his video.

As for why Montana agreed to engage in coitus in front of Pumper's cameras


So far, we're told Pumper has not responded to the letters.