First, check the rent-increase notice, the tenancy agreement and the current rules for your property, including any applicable rent cap or notice requirements. Raise your concerns in writing with the landlord and keep the notice, rent records and relevant messages. If it is not resolved, you can refer the dispute to the Residential Tenancies Board (RTB), generally before the new rent takes effect and within the applicable time limit, often 28 days from receiving the notice. The RTB may offer mediation or proceed to adjudication, with the outcome depending on the facts and evidence; consider checking the latest guidance on RTB.ie or speaking to a solicitor if the issue is complex.