United Airlines announced Friday that emotional support animals will only be allowed on flights that are eight hours or shorter, ABC News reports. “We have seen increases in on board incidents on longer flights involving these animals, many of which are unaccustomed to spending an extended amount of time in the cabin of an aircraft,” the airline said in a statement explaining its decision. This is not the first time United has attempted to regulate emotional support animals: It already only allows cats or dogs that are over 4 months old (although miniature horses still qualify as service animals). And in 2018, after the airline reported that it has seen a 75 percent uptick in emotional support animals, United required human passengers to provide health and vaccination records and promise that their companions would behave.