They rarely go anywhere apart â even on airplanes.  Luna is certified as an emotional support animal, a designation under federal law that allows her â if so desired â to sit on her companionâs lap, instead of being in a cage under a seat, where regular pets must ride. And at a time when airlines are flying at near capacity and charging for seemingly everything but peanuts, Luna rides free.  Classifying animals as emotional support animals has long been permitted under antidiscrimination laws, allowing owners to take them into restaurants and shops or to residential buildings that have no-pet policies. To demonstrate the need for an emotional support animal, the animalâs owner needs a letter from a mental health professional.  But their presence on airplanes is increasingly facing a backlash from flight attendants, passengers with allergies and owners of service animals, like Seeing Eye dogs, who say that airplane cabins have become crowded with uncaged animals who have no business being there. The Department of Transportation does not require airlines to keep data on emotional support animals. One that does, JetBlue expects more than 20,000 emotional support and service animals this year.  âItâs becoming a big problem,â said Marcie Davis, founder of International Assistance Dog Week. âIâve seen people bring on pets and try to pass them off as an emotional support or service dog. Itâs not appropriate and itâs not safe.â  Ms. Davis, who uses a wheelchair, flies about once a month, along with a service dog, for her job as a health and human services consultant.  âAssistance dogs are trained not to bark in public, not to go smelling other dogs or people,â she said. âIâve had my dog attacked in multiple situations. Honestly, I understand that thereâs some value that people need an emotional assistance dog. But I think a lot of this is that people love their dogs and think they feel like if you have your dog, why canât I have mine?â Airline workers echo Ms. Davisâs view. âItâs out of control,â said an American Airlines flight attendant, who spoke only on the condition of anonymity because she was not authorized to speak publicly.  The attendant, a 30-year airline veteran, recalled one passenger whose dog, while not big enough to throw a saddle on, filled the entire seat area, its paws and tail spilling over the arm rests. It was more hospitable than the cargo hold, though, where animals without the emotional support or service designation must ride if they are too big to fit in a cage under a seat.  She did not approach the passenger about removing the dog from the cabin because it was perfectly acceptable where it was.  For that matter, so would have a cat, a monkey, a miniature horse or even a potbellied pig, if they were certified. The Air Carrier Access Act allowed for emotional support animals to be taken on planes, broadening the American Disabilities Act, which recognized service animals in public places, said Robert Farr of the Pacific A.D.A. Center.  Airline employees are often reluctant to question passengers with emotional support animals for fear of violating the law or stirring a conflict, the flight attendant said. This week, for example, a blind man and his Seeing Eye dog were removed from a US Airways flight after a dispute erupted over securing his service dog while the plane prepared for takeoff. The airline said the passenger was removed because he had become abusive to a flight attendant.  There are many passengers with the emotional support certification who cannot imagine flying without their pet. Ms. Griffis, who has written about the issue on her blog, said that Lunaâs presence was instrumental in weaning herself off antidepressants. Ms. Griffis, a former Colorado resident, said in an interview from Paris that she was not afraid of flying and that Luna was more comfortable traveling in a cage. Still, she added: âhaving Luna with me really provides a level of comfort. When Iâm on the road, I am safe, no matter if Iâm in Germany or Mexico.â  Airline websites have detailed policies on animals, typically allowing for cats and dogs that can fit in a carrier (approximately 18 by 12 by 8 inches) that slides under the seat. Delta says it allows rabbits, guinea pigs, hamsters, birds and marmots. But airlines charge fees, ranging from $75 each way on Southwest to $125 on American, Delta and United.  Emotional support animals, by contrast, travel free, and restrictions on their size and species are left to the airlinesâ discretion. They are not required to be caged. And unlike service animals, which undergo extensive training, they require no training. Their task is to provide comfort to their companions.  To serve the needs of the animals and their owners, a cottage industry of websites and doctors advertising documents that certify emotional support animals has emerged.  Carla Black, a psychotherapist in Marina del Rey, Calif., began receiving enough requests for emotional support animal certification that this year she began advertising on her website. For $99, she provides an hour of her time, over the phone or Skype, and a clinical assessment, along with a prescription letter, which is valid for one year.  Ms. Black said in a telephone interview that before she issues a letter she ensures the client is eligible under criteria set by the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition. âI make sure they qualify for depression or whatever, P.T.S.D.,â she said, referring to post-traumatic stress disorder.  There are also myriad places on the Internet that cater to the growing demand, including a robust market for service animal vests.  Occasionally, the needs of passengers with support animals collide with the needs of other passengers, like those with allergies. In those cases, courtesies like switching seats can address the issue, passenger advocates say.  Ms. Griffis, acknowledging that more people are traveling with emotional support animals, said it was important for animals to be well behaved.  As for skirting the rules?  âShame on anybody who abuses the system,â she said. âThatâs why I tell people this isnât just about getting around airline fees. If you genuinely need this animal in your life, thatâs what this is about.â
A growing number of fliers are accompanied by pets legally certified as emotional support animals, sometimes raising eyebrows, and doubts.