“Probationary tenancy” is not generally a separate legal category in Irish residential tenancies. A landlord must follow the rent-review rules, which usually limit reviews to once in any 12-month period and require the correct written notice and supporting information. If your tenancy began less than 12 months ago, an increase may not be lawful, but the position can depend on the tenancy’s dates, property and applicable rent-control rules. Check the latest guidance on the RTB or gov.ie websites; the RTB can ultimately decide a dispute based on the individual facts.