My friend experienced something like this, except much worse. When she told them she wasn't going to renew, they basically said that if she goes to a school within a certain distance of their school they'd give her a really bad recommendation. She taught in a small town, so she basically had to move somewhere else.
To be honest, from what you said they're doing to you, it doesn't seem so bad. Until it gets much worse, I'd just keep your head down and do the work. I don't know about your experience there, but I'd imagine you want to leave on good terms. I mean really, what else can you do? If you aren't considering quitting, then all you can do is do what they ask and just be happy when you go!