(1) When the fair rent of a building has been fixed under this Act, no further increase in such fair rent shall be permissible except in cases where some necessary addition, improvement or alteration has been carried out at the landlord's expense :
Provided that the fair rent as increased under this sub-section shall not exceed the fair rent payable under this Act for a similar building in the same locality with such additional improvement or alteration and it shall not be chargeable until such addition, improvement or alteration has been completed :
Provided further that any dispute between the landlord and the tenant in regard to any increase claimed under this sub-section shall be decided by the Rent Control Court.
(2) Where, after the fair rent of a building has been fixed under this Act, there is a decrease or diminution in the accommodation or amenities provided, the tenant may claim a reduction in the fair rent as so fixed, and any dispute between the landlord and the tenant in regard to any reduction so claimed shall be decided by the Rent Control Court.