In NY a tenant is allowed to a family member, which would include a live-in boyfriend, move into the apartment, even if the landlord does not consent. Therefore, if you are in NY you may not be able to do anything about it. However, you can advise the tenant that because of the "guest" you will not be renewing her lease when it comes due. This may get her to follow the rules you have laid out to her. Obviously, if her lease has previously expired and she in now a month-to-month tenant you can serve her with a notice of termination and subsequently evict her if she does not move out.
Answered on Feb 25th, 2014 at 4:53 AM