Query related to joining client company

[curiousgeorge9]

I am working for consultancy firm and working at client location. My client is willing to hire me but there is a clause between my employer and client that they cannot hire me. I am working with this client for more than a year on my employer's payroll but I have not signed any documents like NDA, Non compete etc.Can I join my client on their payroll? I have GC from my current employer, Can they revoke my GC? or Can they take any legal actions for me joining the client? If yes, how can I protect myself from any legal issues.