Check whether the increase follows the rent-control rules applying to your tenancy, including the permitted amount, timing and notice requirements. Ask your landlord in writing for the calculation and keep the rent notice, tenancy agreement and payment records; do not simply stop paying rent. You can raise the matter through the Residential Tenancies Board (RTB) dispute resolution process, using its current guidance and rent calculator where relevant. The RTB or a solicitor will assess whether the increase is lawful based on the facts of your tenancy.