If you believe that your landlord is breaking a law or violating a regulation, you can call 311 to find out which city agency may be able to assist you. There may be more than one. But if you report your landlord and are in a non-regulated apartment, the landlord isn't likely to renew your lease. Terminating your lease may be deemed as retaliatory eviction, which is prohibited, however these are difficult cases to win. To begin with, if your complaint doesn't specifically relate to your rights as a tenant, your situation might not fit the criteria for a retaliatory eviction case. While a tenant's attorney may be able to negotiate a renewal, there's no guarantee and you'll have to pay legal fees. For example, reporting that your landlord is renting out an illegal basement apartment won't do you any good, unless those neighbors are in some way directly impairing your rights, by being noisy, compromising your safety, etc. So think twice before you file a report just because you have a strained relationship with the landlord. Vengefulness isn't a good idea.