Non-compete

[Justice for opt student]

I am currently in my STEM OPT Extension. I was working with a consultancy as a contractor and was working at a client for that consultancy with following relation Consultancy -> Prime-Vendor -> Company. The client company offered me a Full time position in their company and I took the opportunity. But, the consultancy people threatening me that I have signed a Non-compete agreement with them and I cannot work with their direct or in-direct client for at least 12 months after my termination. But, I was confused like I am in OPT and they didn't even sponsor my VISA. How can a student under OPT can be restricted from working as it is considered as a training. Now, they are threatening me they will send a notice for vendor,client and me that I've violated that agreement. I don't know how to defend myself against this case. 

Please, help on this issue 

[pontevecchio]

If you signed a contract, run it by a Labor Lawyer in your state.