The companies buy and compile housing court data from the state Office of Court Administration. Landlords, in turn, use the information to screen prospective tenants, often rejecting those who have been to housing court. But the information is frequently incomplete, misleading or wrong, according to housing advocates and tenant lawyers. For example, a tenant who withheld rent because of atrocious living conditions like rats or mold could end up blacklisted, even if he prevailed in court.

“Tenants should have the right to be able to go into court to protect themselves when their landlord is doing something wrong, without facing discrimination afterward,” said Benjamin J. Kallos, a New York City councilman who sponsored legislation that would bar landlords from discriminating against tenants on the lists, except in cases where the tenant has not satisfied the terms of an order issued by the courts.