Let's say you rent an apartment in a building or house where three or more families live. If the owner/landlord doesn't have a Certificate of Occupancy that describes or permits your living quarters, he or she can be restricted from collecting rent in a law suit. However, applying the rules governing these situations is a complex Landlord Tenant matter. As always, there's no guarantee a judge will rule in your favor, even if the landlord hasn't abided by New York State and NYC building laws. Consequently, implementing this defense successfully generally requires you to retain a tenants' attorney, rather than attempting to go it alone.