I'm a dance instructor working for a studio with no contract. I'm currently teaching two group classes per week at $25. per class. In addition, I've been asked to line up other opportunities in the community for classes and recruit clients everywhere I go and print flyers and distributed where ever I can. I have been doing this for over a year with no payment or commission for my sales work. In addition, I have been assigned NO private clients. The studio claims there's not enough work but also threatens to cut me loose if I teach elsewhere.
Is this normal for the industry?

As a freelance teacher, you are under no obligaton to them ,as they have non to you.

The upside of this is.. you may teach anywhere without restraint. In fact, thats what you should do. Find a venue and promote you own classes.