American Airlines has become the latest carrier to further crack down on emotional support animals and limit them to cats and dogs older than four months.
The move follows similar restrictions on puppies and kittens introduced by United Airlines and Delta Air Lines.
But those with a legitimate need for a trained service animal will still, in some limited circumstances, be able to bring a miniature horse on board.
Examples of service animals include seeing-eye or hearing assist dogs specially trained to assist a disabled person.
Emotional support animals fall into a looser category of an animal, not necessarily trained, used to assist the emotional well-being of a passenger.
Under US Department of Transportation regulations, these animals fly free of charge and American found that the number of emotional support animals it was carrying grew by 48 percent from 105,155 in 2016 to 155, 790 in 2017.
More than 70 percent of these in 2017 were dogs and just 3 percent were cats..
US carriers moved in 2018 to exclude a range of emotional support animals after an increase in the number of incidents where people were bitten or animals defecated in the cabin.
Cabin crew also reported aggression between some animals and questions were raised about the impact of untrained animals on evacuations.
People were also increasingly bringing on board animals other than dogs and cats and United Airlines moved to introduce restrictions after a woman tried to bring a peacock on to a flight as an emotional support animal.
Other instances in recent years have involved a turkey, a pig and a duck.
A survey by American of 18,000 people found 58 percent believed that only trained service dogs should be permitted in the cabin.
Nine out of 10 said passengers should be limited to just one emotional support animal and 96 percent said the animals should have up-to-date vaccinations.
American said on its website that it would introduce the new guidelines from April 1 but did not elaborate on the circumstances in which a miniature horse may be brought on board.
It said the ban on kittens and puppies extended to both emotional support and service animals.
“Animals under this age usually have not received the necessary vaccinations that protect team members and customers,’’ it said.
Customers may only bring one emotional support on board and the airline will require documentation to include a veterinary health form as well as immunization details.
“American supports the rights of customers, from veterans to people with disabilities, with a legitimate need for a trained service or support animal,’’ the airline said.
“Unfortunately, untrained animals can lead to safety issues for team members, customers and working service and support animals onboard aircraft.”