United Airlines is updating its policy concerning emotional support animals allowed on its flights.

The carrier says that it will no longer allow flyers to bring emotional support animals other than dogs or cats, and that the animals must be at least 4 months old or older to qualify.

In a statement from the airline, United says that starting Jan. 7 only cats and dogs will be allowed on United flights as emotional support animals.

“We are limiting acceptance of emotional support animals to dogs and cats. Additionally, we are limiting acceptance of service animals to dogs, cats and miniature horses.”

“We are limiting emotional support animals to flights under 8 hours. We have seen increases in onboard 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,” United added in its statement.

All of these changes go into effect on Monday, Jan. 7. The airline will honor reservations affected by these changes that were made prior to Jan. 3, as long as the animal is covered under the previous policy and has the right documentation.