DOJ's examination of the merger turned up concerns regarding routes between United's existing hubs and Continental's hub at Newark. The companies agreed to transfer some takeoff and landing slots to Southwest Airlines to allay the concerns. With that potential antitrust violation removed, Oberstar said Justice believed it had no legal grounds on which to oppose the transaction.

"This action points strongly to the need to give broader authority over such mergers to the Department of Transportation, allowing DOT to consider such factors as the impact a merger will have on service to communities and customers, as well as the effect the merger could have on the industry as a whole," Oberstar said.