zlacker

Business owners and managers talk. I've heard of unofficial (and very illegal) blacklisting being a thing in NYC in the past, for multiple industries.

Collusion between employers to ensure that non-competes are enforced sounds very plausible, given that it is legal.

I think that the existence of a non-compete may also be a liability for the new employer, and it's not solely a practice meant to remind labor of what their place is.