Your emotional support animal in training may not get to fly business class anymore.

Or any other class, for that matter.

United Airlines is changing its policies regarding emotional support animals, banning animals under the age of 4 months from the cabin, “to further ensure the well-being of our employees and customers while accommodating passengers with disabilities,” the company said in a blog post on Thursday.

“This is just another move in a long line of moves to restrict pets on aircrafts,” said Christopher Elliott, founder of consumer advocacy organization Elliott.org. “Animals could go the way of peanuts on planes at some point in the future — ideally airlines do not want to have any animals in the cabin.”

The new policy will go into effect on Jan. 7 and comes weeks after Delta Air Lines made a similar change. “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. The airline did not respond to a request for additional comment.

United will also limit animals allowed on flights, banning all emotional support animals that are not dogs and cats. Service animals, which unlike emotional support animals are trained to assist a qualified person with a disability, are still accepted on flights as long as they are a dog, cat or miniature horse, the new policy said.

This comes after United turned away one passenger in January 2018 for attempting to board with her “emotional support peacock,” for whom she had purchased a ticket.

The number of animals in the cabin has been on the rise in recent months, despite the fact that Delta, American and United Airlines have tightened paperwork requirements on emotional support animals. Most service animals, which are trained to assist a qualified person with a disability, are still accepted on flights

Delta said it had six biting incidents in a period of two months in early 2018 and the number of “animal incidents” on planes, ranging from urination to barking and biting, has increased 84 percent since 2016, Delta chief operating officer Gil West told The Wall Street Journal in August.

The airline carries an average of 700 emotional support animals per day on flights, up from 450 a day in 2016, West said.

Delta banned pit bull dogs from flights in July 2018 after a dog scratched a flight attendant, and United Airlines banned dozens of breeds of dogs from flights in May 2018, including bulldogs, Boston terriers, all kinds of pugs and boxers, Shih Tzus, mastiffs, American bully, pit bulls, American Staffordshire terrier, and Pekingese. Many of these breeds have been found to suffer respiratory problems on flights.

Elliott said the rise in animal passengers reflects a larger shift in how people view their pets — one airlines are struggling to combat.

“The role pets play in society has really shifted in the past couple years,” he said. “When people think of pets as children, they will do anything to fly with them. But pets should really stay at home.”