Under a new rule, the Department of Transportation says it will no longer recognize emotional support animals as service animals, paving the way for airlines to deny the pets free flights.

According to ABC News, in a revision to its Air Carrier Access Act, the DOT defines a service animal as a "dog, regardless of breed or type, that is individually trained to do work or perform tasks for the benefit of a qualified individual with a disability." Airlines are "not required to recognize emotional support animals as service animals and may treat them as pets," it stated.

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In the past several years, there have been several complaints as passengers brought animals like peacocks, pigs, and miniature horses on planes as emotional support animals. The DOT says "the disruptions caused by requests to transport unusual species of animals onboard aircraft, which has eroded the public trust in legitimate service animals," which are typically dogs.

Airlines have been looking for ways to crack down on what they say are abuses of the support animal rules. The DOT says there have been an increase in complaints from other passengers due to the misbehavior of ESAs.

According to ABC News, in 2018, the number of passengers traveling with an emotional support animals increased 14%, following a 60% increase the year before.

Passengers can still travel with pets under their airline carrier's pet policy, which usually costs around $125 each way to carry-on a small pet.

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