There are some MLW wrestlers not being allowed to work AEW due to a clause in their contracts. One prime example is that MJF was working for both promotions until his MLW deal expired, and now is with AEW full time. Brian Pillman Jr. has been working some AEW shows but will return to MLW when the promotion resumes TV tapings.
According to Fightful Select, several wrestlers, like Brian Pillman Jr., who had contract disputes will still be working the tapings. The language in prior MLW contracts didn’t keep wrestlers from wrestling in AEW because the company didn’t exist when they were signed.
Other companies, however, will not let their wrestlers appear on other North American televised wrestling shows. AEW has contracts like that, which is why Jon Moxley can appear for NJPW in Japan, but not any shows in the United States.
Some of the wrestlers on the MLW roster were offered new deals earlier this year which would keep them from AEW, but they passed on them.