Actually, the law is very specific.  Only dogs can be service animals.  The rest are classified as "comfort" animals, and businesses, airlines, etc. are not required by the law to accomodate them.  The may choose to like the airlines, but it is not required.  This is a pet peeve of mine.  These cheaters are making it more difficult for those who are in real need.  It's time to license them so there is no question.  Kinda like handicapped parking... I can't just say I have a disability, I have to apply for a handicapped permit and display it when using that parking.  Licensing would solve the problem for everybody... another simple solution that should have been enacted a long time ago IMO.  This situation would never have happened.