Ask the landlord in writing to explain the increase, and keep the rent review notice, tenancy agreement, payment records and relevant dates. Check the RTB’s guidance to confirm whether the property was covered by RPZ rules at the time and whether the required notice and rent-setting information were provided. Do not withhold rent without advice; contact the RTB or Threshold and consider using the RTB’s dispute resolution process to challenge the increase. The outcome depends on the facts of the tenancy, and a solicitor can advise on more complex cases.