A new rule announced Wednesday by the U.S. Department of Transportation will allow airlines to limit the types of animals that fly in the cabin for free under the classification of emotional support animals.

The DOT defines a service animal as a “dog, no matter what 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 no longer required to recognize emotional support animals as service animals, causing them to likely be treated as pets.

Airlines have been wanting to crack down on travelers abusing emotional support animal policies. Typically, service animals are dogs, but airlines have seen a variety of animals being brought onto planes by passengers as emotional support animals, including miniature horses, turtles, hamsters, pigs, and birds.

The practice has “eroded the public trust in legitimate service animals,” the DOT said in its rule, which it said was prompted in part by an increase in travelers “fraudulently representing their pets as service animals” to avoid charges for transporting pets.

“The Department of Transportation’s final rule will protect the traveling public and airline crewmembers from untrained animals in the cabin, as well as improve air travel accessibility for passengers with disabilities that travel with trained service dogs,” Airlines for America President and CEO Nicholas E. Calio said in a press release.

The new rule will go into effect 30 days after it is published in the Federal Register. That date has not yet been set.