Nassau County does not have a no-pet lease clause waiver law. These laws are in NYC and Westchester. Tenants should consult with an attorney who can still make legal arguments for the keeping of an animal in Nassau County, even if the tenant has a no-pet lease clause.

If you are a rent stabilized tenant, the terms of your original lease cannot be changed to remove rights and you normally would be entitled to a renewal lease under the same terms and conditions as your original lease. If the lease contained no restrictions on the keeping of dogs and no language allowing the landlord to promulgate rules on the keeping of dogs, it is unlikely that you could now be required to use a muzzle (unless your dog has attempted to bite someone). If you are not a rent stabilized tenant, when your lease expires your landlord could choose not to renew your lease. That sometimes happens for a variety of reasons, including when a tenant does not comply with the demands of the landlord (even if the tenant believes the demands are unfair). Sometimes when coops promulgate rules, they don't follow procedures specified in their by-laws or by law. In these instances, the shareholders can challenge the rules. This is something your landlord can consider doing. Even though it appears you are being singled out, a discrimination case is normally one based on race, religion, ethnicity, age, sexual orientation, disability, and the like, not the keeping of a dog. The letter you described would probably not be considered harassment under the law. I suggest you consult with a landlord/tenant attorney who can review the matter more thoroughly and advise you further.