Usually, a rent increase above the applicable Rent Pressure Zone limit is not lawful unless a specific statutory exception applies. The permitted limit and exceptions can depend on the tenancy’s start date, the property’s status and whether the rent is being set for the first time, so check the current RTB guidance and calculator. Ask the landlord in writing for the calculation and legal basis for the increase. If you cannot resolve it, you can bring the issue to the RTB, whose decision will depend on the individual facts; a solicitor can also advise you.