ORLANDO, Fla. — United Airlines is the latest to crack down on the use of emotional support animals on flights. 

United Airlines announced this week that it would only consider cats and dogs as emotional support animals on flights. Also, only dogs, cats and miniature horses will be accepted as service animals on flights.

Airline rules for emotional support and service animals have in the past been broader than the standard definitions from the federal government.

In fact, the Dept. of Transportation says airlines do not have to allow support animals in the cabin if they are too large, heavy, disruptive or are threatening to people on board, nor do they have to accept certain kinds of animals, like ferrets or snakes.

As the number of people bringing emotional support animals on planes has skyrocketed, other airlines have limited the kinds of species that can be ESAs. United's decision to date is one of the strictest though.

In addition, United is banning ESAs on flights longer than 8 hours, saying the pets are normally not accustomed to flights so long.  The airlines is also no longer allowing puppies or kittens under 4 months of age on flights, because they will not have had any necessary vaccinations yet.

The new policy starts Jan. 7, but they will honor reservations made prior to Jan. 3.