A rent increase notice that is late, missing required information or not properly served may not take effect as stated. Generally, the landlord must give at least 90 days’ notice, include the prescribed details and send a copy to the RTB on the same day, although other rules may also apply. Write to the landlord promptly, explain the problem and keep the notice, tenancy agreement, payment records and all messages. Do not withhold rent without advice, but ask Threshold, Citizens Information or a solicitor whether you should continue paying the existing amount. The RTB can ultimately decide the notice’s validity based on the tenancy’s facts.