Aeromexico, which has 18 weekly flights from Mexico City that cross U.S. airspace on their way to Europe, said that the U.S. proposal might violate international transit agreements and that it is consulting with the Mexican transportation department to "present our legal position for this potential requirement."

"This potential directive will restrict our privilege to fly across U.S. territory without landing, and to land for non-traffic purposes," said Fernando Ceballos, Aeromexico's assistant director for airport operations, in an e-mailed statement. If the TSA issues the requirement, he said, it would not be practical to fly around the U.S. coast. "Flying over water along the coast is not an option for Aeromexico as increased flight times would be prohibitive given the type of aircraft we use, our slots and crew requirements."