"The first thing this guy asked me is, 'Is that a real service dog?'" Haag told ABC News. "I just find that question kind of odd because nobody at the airport has asked me that and I fly all the time. I said, 'Yes.'"

"I then tell him I called eight days ago, registered him with your disabilities department," Haag told ABC News. "I flew out here three days prior on the same airline, and I didn't have any issues."

The American Humane Association issued a news release about the incident, saying the airline requires only one of the following forms of identification for a service dog to board a flight: an animal ID card, a harness or tags, written documentation or verbal assurance. The AHA said Axel had been wearing a service vest and the airline received "credible verbal assurance" from Haag, so the requirements should have been met. 

"We apologize to both Captain Haag and his family for the confusion with the travel plans yesterday," spokeswoman Victoria Lupica said. "Thank you, Captain Haag, for your service to your country. We are extremely proud to fly you, Axel and your family."