During the start of AACS, Bob Weatherly (VP ops Atlas) told us that EU law precluded the AACS crewmembers from being in an American Union. We were pretty sure at the time that this was BS but who knows.
Even if it wasn't BS at the time, it is now. AACS has devolved into AABO -- "Atlas Air Branch Office." As far as I can tell, they are no longer a UK company...