Legal Concerns Regarding Non-Compete and H1B Transfer

[nightcrawler]

I am currently on an H1B visa and was employed by a consulting firm (Employer A). I signed a non-compete or similar agreement with them. Recently, a competitive vendor (Employer for the same client offered me a job. I resigned from Employer A, joined Employer B (still working for the same client), and successfully transferred my H1B.
Now, Employer A has sent a notice to my lawyer claiming breach of contract and is seeking penalties.
My questions are:
Is such a non-compete or penalty clause enforceable under U.S. law, especially for H1B workers in a consulting/client setup?
What are my legal options and risks in this situation?
How should we respond to the notice from Employer A?

[Anta Assamey]

[nightcrawler]

Urgent Help