Can my current vendor enforce Non Competition actions against me?

I am a IT consultant working on corp. to corp. basis through vendor at the client. My contract agreement dated back in 2006 for my first Purchase Order restricted me for working for the same client for 180 days after termination of my contract. In three months of compelting intial contract I got another offer from the same vendor to do another contract for this client. Now this contract going to the end. The second Purchase Order did not have contract attached, I guess they assume old 2006 contract is still in effect.
After my contract will be ended vendor still does not want to release non compete restriction for work for this client even if these jobs not available to vendor to fill in.

Is there a chance to fight non compete ion this case?

I doubt vendor will go after me.