That's... not a cartel though? A cartel is a group of firms conspiring to artificially control the supply of some good in order to increase its price, what you described is just several independent firms that have a high demand for workers and are bidding up salaries for them.
It was more cartel-like when Apple and Google were conspiring to keep tech salaries down by setting salary caps.
It was more cartel-like when Apple and Google were conspiring to keep tech salaries down by setting salary caps.