It is most definitely not discrimination if having having a guest's pet on your property affects your business!
We had a guest a few years ago who asked me where and how our linens are laundered and stored as she was so badly allergic to cats and dogs.
We dont allow our 3 cats and dog into our guests houses to protect our guests with allergies. So we never allow a guest to bring a pet with them. We are not discriminiating against anyone! We are protecting future guests and our business.