As the species of service and emotional support animals have become more diverse, airlines have had to make some tough decisions. Birds, monkeys, and snakes have been barred from boarding airplanes with passengers, but even more conventional pets like dogs have been rejected based on their breed. A new rule from the U.S. Department of Transportation (DOT) aims to change that. As Travel + Leisure reports, the agency now forbids airlines from discriminating against service dogs of particular breeds, including pit bulls.

Last year, Delta banned all pit bulls from flying, regardless of whether or not they were certified therapy animals. United Airlines also banned pit bulls last year, along with 20 other dog breeds, including pugs, bulldogs, mastiffs, and shih tzus.

Under the new DOT guidelines, these policies are no longer legal. The statement reads: "The Department’s Enforcement Office views a limitation based exclusively on breed of the service animal to not be allowed under its service animal regulation. The Enforcement Office intends to use available resources to ensure that dogs as a species are accepted for transport."

The new rule applies specifically to service animals, or animals that have been trained to perform a job that's essential to their owner's wellbeing. Emotional support animals, which don't require special training and aren't covered by the Americans With Disabilities Act, don't qualify.

Even if a pet is a certified service animal, airlines still have the right to reject them in certain cases. Air travel companies can request documents related to an animal's vaccination, training, or behavior history. If they find anything in the papers that indicates they're not safe to fly, airlines can turn them away on that basis.

In the same statement, the Department of Transportation clarifies which species of service animals should be allowed on flights. Miniature horses are now included on the list of service animals airlines must allow to fly, while ferrets, rodents, snakes, reptiles, and spiders are the only species airlines can ban outright.

[h/t Travel + Leisure]