I recently saw a story about a woman trying to board a plane with a squirrel. You might think that’s nutty, but United Airlines reports that requests for emotional support animals increased by 77% last year.

As more people try to bring their animals with them wherever they go, employers are asking more questions about animals in the workplace. Most employers understand that they must accommodate requests for some animals, but which ones? Under what circumstances?

In the United States, the Americans with Disabilities Act (ADA) indeed requires most employers to allow service animals in the workplace as a reasonable accommodation to employees with disabilities. However, the ADA actually defines “service animal” very narrowly. Under the ADA, only dogs (and in some cases miniature horses) can qualify as service animals. An emotional support peacock, for example, won’t fly.

In fact, “emotional support animals” are not covered by the ADA at all. There is a sharp difference between service animals and emotional support animals under the ADA. Service animals must be individually trained to do work or perform tasks for people with disabilities. Examples include guiding people who are blind, alerting people who are deaf, pulling a wheelchair, or calming a person with Post Traumatic Stress Disorder (PTSD) during an anxiety attack. A dog that provides only emotional support or comfort does not qualify under federal law. It’s worth noting, however, that some states, such as California, may require emotional support animals to be permitted as a reasonable accommodation.

When an employee asks to bring a qualifying service animal to work, the employer generally must allow it unless the animal causes an “undue hardship.” If the dog causes a safety hazard or prevents coworkers from doing their jobs, the accommodation likely wouldn’t be reasonable.

Things gets particularly hairy when one employee is allergic to another employee’s service animal. The Department of Justice’s Disability Rights Section (DOJ) has stated, “Allergies and fear of dogs are not valid reasons for denying access or refusing service to people using service animals.” The DOJ suggests assigning those employees to different locations of the facility or separating them if they must be in the same room. If an employer allows emotional support animals even though it’s not required by the ADA, the issue of an employee being allergic to that animal becomes even more complicated.

If you have questions about service animals in your workplace, you should seek the advice of an attorney, because sometimes the answers are fuzzy.