If the increase is valid and legally due, continuing to pay only the old rent can leave the tenant in rent arrears. The landlord cannot evict or lock out the tenant immediately, but may follow the formal notice and dispute procedures required by Irish tenancy law. If the increase appears invalid—for example, because the notice or amount does not comply with the applicable rules—keep paying the undisputed rent and seek advice rather than stopping payments altogether. The RTB or a solicitor would assess any dispute based on the tenancy’s particular facts.