The Ellis Act is a state law which says that landlords have the right to evict tenants in order to “go out of business”. All units in the building must be cleared of all tenants- no one can be singled out. Most often it is used to convert to condos or group-owned tenancy-in-common flats. Once a building becomes a condo it is exempt from Rent Control, regardless of the age of the building, and even if a unit owner subsequently rents to a long-term tenant.
See this project by the Anti-Eviction Mapping Project HERE