dablindfrog wrote: in this case,there are no penalties in my contract
So if there is no statement of penalty for breach in your contract then you better fill me in again on what exactly you have been penalized and how? If there is no penalty clause in your contract then I can't see any reason that you could not get this money back by appealing to the labor board. You would very likely win this one and you wouldn't be the first to get a win against an employer who has acted inappropriately.
dablindfrog wrote: where do you draw a line?if they asked me my past 10 months salary back,would this be ok?
If you signed an employment contract that stated that if you breached you agree to pay back all the money that you had earned up to that point then I can't see any legal reason that the school could not enforce their rights to collect that money. I am not saying that it is ethical for them to include such a large penalty, but then you should never have agreed to it in the first place.
I think that a lot of people overlook the fact that a written contract is an easily enoforceable legal agreement. It cannot force you to do something against the law, but provided that it is within the law then it is binding which is why you should read and understand any contract carefully before you sign. Far too many people gloss over the details and just sign up to get the job, only to turn around and complain when the school actually enforces the terms of that contract.
In regards to your ten month back payment example above, I would be quietly confident that you could have that one overruled as being unreasonable, but even if you did then you would still need to negotiate a penalty payment which would probably end up being in the order of two or three months.