If you believe a rent increase is unlawful or the notice is invalid, raise the issue with your landlord and keep copies of all correspondence. You can generally refer a rent review dispute to the RTB within 28 days of receiving the rent review notice, so check the current RTB guidance promptly. The RTB may offer mediation or arrange adjudication, where it will consider the tenancy documents, notice and relevant rent information. The timeline varies, and the outcome depends on the facts of your case; a solicitor can advise on a complex dispute.