Alaska Airlines will become the first US carrier to ban Emotional Support Animals (ESAs) on its flights.

Starting on January 11, Alaska Airlines will only allow trained service dogs and refuse transport to any other ESA. The decision follows a ruling by the Department of Transportation from early December that says that airlines will not be required to recognize ESAs as service animals, and may treat them as pets.

Until now, the agency hadn’t defined what, exactly, was a service animal, meaning all animals were allowed aboard, including pigs and peacocks.

In a news release, Alaska Airlines said, “Following recent changes to U.S. Department of Transportation’s (DOT) rules, Alaska Airlines will no longer accept emotional support animals on its flights. Alaska will only transport service dogs, which are specially trained to perform tasks for the benefit of a qualified individual with a disability.”

The airline requires service dogs not be so large as to exceed the footprint or personal space of a guest’s seat or foot area, must be leashed at all times, and cannot be under four months old.

“This regulatory change is welcome news,” said Ray Prentice, director of customer advocacy at Alaska Airlines in the news release, “as it will help us reduce disturbances onboard, while continuing to accommodate our guests traveling with qualified service animals.”

Passengers who booked a flight before January 11 with an ESA will still be allowed to bring the animal aboard until March 1.