New rent pressure zones have been introduced in 19 areas across 11 counties.
This includes all of Co Meath, Co Louth and Limerick's metropolitan area.
A rent pressure zone (RPZ) is a designated area where rents cannot be increased by more than 4% per year.
This applies to new and existing tenancies, unless an exemption is being applied.
These come on foot of a new Residential Tenancies Board (RTB) Rent Index Report, which shows the national average rent stands at €1,169 per month.
This is an 8.3% increase - or €90 - annually and 2.1% quarter-on-quarter.
While growth remains high in Dublin - with the standardised average rent of €1,662 per month - an increase of 8.5% (€70) on the previous year rental inflation has been highest in areas outside the Greater Dublin Area, with an increase of 9.6% year-on-year.
"It is important to note that there continues to be a divergence in rent growth between new and renewed tenancies with the standardised average rent for new tenancies €1,245 per month compared to €984 for renewed tenancies", RTB adds.
Housing Minister Eoghan Murphy says: "This is the most significant expansion of rent controls since the rent pressure zones were first introduced two years ago.
"Nineteen new areas will now come under the 4% annual cap.
"It is a direct result of the new rent reforms that were introduced into law last month.
"We brought these changes in because while our rent controls are having an impact, they are clearly needed outside of Dublin and in other existing high rent areas. Because of these changes roughly 65% of renters are now covered by rent controls."
"Rents are still too high and in some parts of the country are still rising unsustainably.
"This was anticipated and that's why we moved to change the criteria for RPZ designation."
Meanwhile, important parts of new rental legislation have kicked in - giving the RTB the power of investigation and sanctioning.
There are three areas where the RTB will be able to use these powers: breaches in relation to rent pressure zones, false and misleading notices of termination and new investigative powers for non-registration of a tenancy.
The introduction of these new powers give the RTB a direct regulatory role in the rental sector.
Sanctions can range from a caution all the way up to a fine of €15,000.
Commenting on the new powers for the RTB, its director Rosalind Carroll says: "We welcome this significant new role for the RTB within the rental market.
"The ultimate goal of these new powers is not about the sanction but to get to compliance and ultimately have a more effective and functioning rental sector."
Further information is available by contacting the RTB or visiting its website.