I'm unsure about the legal situation re educational establishments in China holding back a foreign teacher's pay. That said, I believe it is a rare occurrence here in China.
Before the start of this semester, a uni in Jixi city of Heilongjiang tried to pull that stunt on me. My recruiter said that was on account of a former foreign teacher there having done a runner, so causing the uni to become distrustful of foreign teachers en masse. When 'the runner' entered into the discussion, I immediately lost interest in the post.
I'm just wondering how one can enter into a contractual agreement with an employer whose contract states that it is signed 'in the spirit of mutual trust and cooperation', while the employer's proposed action confirms he does not go along with the first of those worty sentiments.
In any case, foreign teachers having done runners is enough of a red flag to wane my enthusiasm drastically re working for any employer who has 'lost' a foreign teacher in that sad way.
Good luck, all the same - the situation where you are needn't necessarily be bad in other ways apart from the holding back of part of your monthly salary payments. But like me, many a foreign teacher wouldn't be prepared to take a chance on that!