The days of pets flying with their owners in airplane cabins for free are coming to an end.

The Department of Transportation issued a final rule Dec. 2 covering animals on airlines. It decided that only dogs can fly as service animals, and companions that passengers use for emotional support don’t count.

The rule aims to settle years of tension between airlines and passengers who bring their pets on board for free by saying they need them for emotional help. Under a longstanding department policy, all the passengers needed was a note from a health professional.

Airlines argued that passengers abused the situation to bring a menagerie of animals on board including cats, turtles, pot-bellied pigs and, in one case, a peacock.

The agency said it was rewriting the rules partly because passengers carrying unusual animals on board “eroded the public trust in legitimate service animals.” It also cited the increasing frequency of people “fraudulently representing their pets as service animals,” and a rise in misbehavior by emotional-support animals, ranging from urinating on the carpet to biting other passengers.

The Department of Transportation proposed the new rule in January and received more than 15,000 comments. While 3,000 commenters favored dropping protections for support animals, 6,000 spoke in favor of them, including people suffering from depression, anxiety and post-traumatic stress disorder, the department said.

The Paralyzed Veterans of America said the mere presence of a dog, cat or rabbit – even if untrained – can help some travelers, and pet fees of up to $175 one-way are a hardship on low-income people.

The new rule will force passengers with support animals to check them into the cargo hold – and pay a pet fee – or leave them at home. The agency estimated that airlines will gain up to $59.6 million a year in pet fees.

Delta Air Lines says it carried about 250,000 animals including service dogs in 2017 and about 600,000 last year.

Under the final rule, which will go into effect at the end of the month, a service animal is a dog trained to help a person with a physical or psychiatric disability. Advocates for veterans and others had pushed for inclusion of psychiatric service dogs. Airlines will be able to require owners to vouch for the dog’s health, behavior and training. Airlines can require people with a service dog to turn in paperwork up to 48 hours before a flight, but they can’t bar those travelers from checking in online like other passengers.

Airlines can require that service dogs to be leashed at all times, and they can bar dogs that show aggressive behavior. There have been incidents of support animals biting passengers and growling or barking at guide dogs for the blind.

Airlines for America, a trade group for the biggest U.S. carriers, said the new rule will protect passengers and airline employees while helping people travel with trained service dogs.

The Department of Transportation stood by an earlier decision to prohibit airlines from banning entire dog breeds as service animals. That is a setback for Delta Air Lines, which banned “pit bull-type dogs” in 2018, a move that was criticized by disability advocates.

Delta, however, is giving no indication of backing down. In a statement, a Delta spokeswoman said the airline is reviewing the new rule but, “At this time, there are no changes to Delta’s current service and support animal policies.”