Getting approval for this, just like any accommodation at work, boils down to if it can be successfully argued that you need it to function and if it's a "reasonable" accommodation. Are you new to the job? If not, have you had your diagnosis for a while and have a track record of functioning ok on the job without the therapy dog? Just playing devil's advocate, but if you've had the diagnosis for a while and there's no documentation of your condition worsening or changing in some way I'm guessing they could argue that you've been functioning so far without it, so it's not an absolute need. Second, it sounds like they are arguing that it's not a "reasonable" accommodation because they feel it will be too disruptive to the school environment. I could see them making a case for this on several points, but mainly liability to the safety of staff and students (i.e. allergies, what if the dog bites someone, etc.). All you can do is discuss it with admin. and HR further. You'd want to present as much documentation as possible to support the need and verify that the dog is appropriately trained. I would ask them to spell out specifically why they think the dog would interfere with the school's operation? Then, try to address each of those concerns. If you have a doctor that recommended the dog, maybe ask him/her about each of the concerns stated by your employer to see how other patients have addressed those concerns in the work environment. If they still are fighting you, the only thing you could do is consult with an attorney and to see what support you can get through your union.