Can my apartment kick me out after changing the rules?

You are only legally "grandfathered" until your current lease expires. When presented with a new lease, you will be signing a contractual agreement that you will have only TWO pets. You can ASK if they will continue to allow three pets under your new lease agreement. However, they are entitled to refuse your request. At that point, your options are to rid yourself of one pet, or find a different place to live which will allow three pets.