Rent caps in Dublin and Cork, to limit the annual increases in rent, will come into effect tomorrow.
The move comes after President Higgins signed the legislation today.
The Planning and Development (Housing) and Residential Tenancies Act 2016 takes legal effect immediately, but the clauses on rent caps in "rent pressure zones" take effect tomorrow.
The caps could be introduced to other cities and commuter areas from next month, after inquiries by the RTB.