Tony has the story correct. However I would add that the holding company was established with the intent to keep the operating divisions as separate entities.

There were several articles written as to why this was done. The conclusions of all of them were the same. FDX mgmt wanted to protect the airline status of FedEx aka FedEx Express. Thus this would not allow the couriers to join a union. The analyst believed that if RPS was merged intact into FedEx that the airline status would be in jeopardy. This is what makes FedEx different than UPS. FedEx Express is an airline that operates trucks, UPS is a trucking company that operates airplanes. UPS falls under the NLRB and FedEx Express is under the NMB.

Union busting 101.