Colluding to not recruit between those players sounds like an intent to limit (to some extent) employees options, which would reduce upward pressure on wages.
Sorry, I assumed 3 comments = 3 downvotes. Anyway, I was just pointing out that it doesn't match any definition of 'cartel' that I can see. However it's still illegal (but not because it's a cartel).
Colluding to not recruit between those players sounds like an intent to limit (to some extent) employees options, which would reduce upward pressure on wages.
What would you call that?