United Airlines is joining rival Delta in changing its emotional support animal policy.
Like Delta it will not allow support pets on long flights lasting more than eight hours.
The carrier will no longer let kittens or puppies under four months in the cabin as emotional support or service animals.
"Animals under the age of four months typically have not received the necessary vaccinations that help ensure the safety of our employees and customers," United said.’
Rules take effect from January 7 and it will honor any bookings already made as long as passengers have the required documentation.
Emotional support animal categories are restricted to cats and dogs, and cats, dogs and miniature horses for service pets.
Airlines have long complained passengers have gamed the system by using previously lax rules to avoid a fee for in-cabin carriage of pets.
Previously, all that was required for most airlines was a letter from a mental health practitioner which could easily be done for a fee without questions asked.
