California Business & Professions Code section 16600 makes clear that any non-compete provision between employer and employee will not be enforceable under California law
Yep, I've seen contracts where they say "Clause x/y doesn't apply in the State of California" and then the employer try to tell me "Well, it's not a non-compete" .. bullshit. It clearly is.
I got the impression from friends that it was a worse situation in India with relieving letters[0], the way it was explained to me you needed your current companies written permission to start a new job and that is frequently abused.
One thing about California law. If you are terminated involuntarily (1), then you can do whatever you need to do to make a living. Build a competing product, hire your former co-workers, sell to your former customers, whatever. Your previous employer can't deny you future income, not one dime. (1)Involuntarily, except for cause, and those causes must be given in writing at the time you are hired.