Maybe not quite what's being intended by this discussion, but definitely related to hiring blacklists in general (if for a different reason), were Google, Apple

Maybe not quite what's being intended by this discussion, but definitely related to hiring blacklists in general (if for a different reason), were Google, Apple and Adobe agreeing not to hire some of each other's employees.[1] 1: https://www.cnet.com/news/apple-google-others-settle-anti-poaching-lawsuit-for-415-million/ https://www.cnet.com/news/apple-google-others-settle-anti-po...