(NBC News Channel) -- New rules for emotional support animals are set to take effect at United Airlines.
Starting today, United Airlines will only allow dogs and cats to fly with passengers as emotional support animals.
The new rule also bans all support animals from flights longer than eight hours, although service animals with specialized training can still travel on long haul flights.
All dogs and cats traveling on board flights must be at least 4 months old.
Additionally, only dogs, cats and miniature horses will be allowed to fly as service animals.
Although the changes take effect today, United says it will honor reservations made by January 3rd under the old rules.