Can rent increase be re-negotiated?

Dear Bronx Tenant: Your facts are confusing. Your landlord's building cannot be sold to a Cooperative Corporation. The building may be converted to a cooperative corporation. When that happens, tenant occupying apartments are allowed an exclusive period of time to purchase their apartments. A Rent Stabilized tenant is able to purchase or not purchase the apartment at the time of cooperative conversion. Now. Do you mean you rented an apartment from an owner in a Cooperative building and that your landlord sold the apartment to another person? If your tenancy is not rent stabilized, the new owner has freedom to honor the existing but not expired lease until the lease ends. When the lease ends, if the new owner and you come to terms on a new tenancy you make your own business decisions about rent. A tenant renting an apartment from a cooperative apartment owner is a subtenant of that owner. The apartment corporation may have the right to review any request to sublease an apartment.

What do you mean by sub-lease? Your lease remains valid and in effect until it expires regardless of whether the building is sold. The new owner cannot simply raise your rent. As for a raise when the time comes, if you have a free market apartment then the landlord can charge whatever they can get.