The best way to put pressure on them is refuse working for them. Do a runner in the middle of the night after finding another and better job. Tell students and parents. You may need a Chinese speaking friend, though.

Teachers who do runners are low down scum IMHO. They give us all a bad name in China. I have told my young boyfriend who is always moaning about the good job I got for him in Kunming, that if he ever does a runner, don't come slithering back to me on his snake-like belly. Always finish your contract and show you have self respect.