As of March 1, Delta Airlines will be tightening restrictions on what animals will be allowed on flights as "Emotional Support". The airline points to an uptick in animal incidents on their flights including one passenger who was attacked by a dog. Owners will now be required to show proof of health in advance and sign an affadavit on the animals' behavior prior to boarding.
Delta is quick to say that this is not to prevent service dogs from boarding. But they point out that it is easy to go online and find ID cards that say "service animal". They say the need arises from poorly trained animals fighting or becoming aggressive with legitimate trained ones.