Australian farmer, Steve Marsh, lost his organic certification when his neighbor's GMO canola contaminated his crops. It's a tricky situation, because you can't really prevent seeds from blowing.
This case has divided the local farming community, and it's outcome will likely set a precedent for Australia.
This is the exact argument the non-GMO crowd has been making for years. Even if you support GMO crops, those of us that don't have a right to uncontaminated food, but how do you prevent the seeds from spreading?
Monsanto has even successfully sued a Canadian farmer whose crops were unintentionally contaminated with GMO seeds.