Fightful Select reports that current AEW World Champion Will Ospreay owns the rights to the United Empire faction name, which is why he can use it in AEW.
The report also notes that Ospreay trademarked United Empire this past April with some legal help. It was further said that AEW had to create/trademark Bang Bang Gang and move away from Bullet Club Gold as NJPW owns that trademark.
After he brought the United Empire to AEW, Ospreay said he was looking to recruit other members. “Speedball” Mike Bailey and NJPW United Empire’s Francesco Akira were the first two to join.