'Biggest Loser' Star -- I Got Screwed on Tape

One of the hard body trainers from "The Biggest Loser" claims she's feelin' the burn from an exercise video deal gone bad -- and now she's suing the spandex off the company behind the DVDs.

Jillian Michaels claims she should have raked in more than $550,000 in royalties and bonuses from her 2005 instructional tape series "The Biggest Winner: How to Win By Losing" -- instead she claims all she got was a measly $100,000 cash advance.

In a lawsuit filed Friday in L.A. County Superior Court, Michaels claims Genius Products -- the home video company -- utilized "fraudulent and unfair accounting methods so as to avoid paying additional sums."

Michaels also claims Genius refused to sell videos on request "in an attempt to avoid paying Plaintiff additional bonuses."

Now she's looking for some serious jack -- at least $550k -- to "punish [Genius] for wrongdoing."