Check the rent-increase notice carefully, including the notice period, calculation and whether the tenancy is covered by the current rent-setting rules. Compare the proposed rent with the applicable limit and similar local properties, then ask the landlord in writing to explain or review it. Do not simply stop paying rent; if you believe the increase is unlawful or the notice is defective, you can seek information from the RTB and consider opening a dispute within the relevant time limit. The RTB or a solicitor would assess the outcome based on the individual tenancy, so check the latest guidance on the RTB or government website.