Carlow and Macroom have become the two latest areas to be designated as Rent Pressure Zones.
The Residential Tenancies Board has informed Housing Minister Eoghan Murphy that the new designations will apply as of today.
It comes as the board's latest index shows a 7% annual increase in national rents.
Rent Pressure Zone designation means rent increases are limited to a maximum of 4% per year in the areas covered.
More than 20 other areas received the designation earlier this year, across almost a dozen counties.
Rosalind Carroll, director of the RTB, says her organisation knows rent pressure zones are having an impact.
She observed: "The RTB is supporting compliance through public awareness campaigns, online resources and information.
"However, there is no one quick fix for the rental sector and regulation is only part of the answer.
"The market is complex, our research illustrates this and we will be working with the ESRI to gain further insights into the factors driving rent inflation."
Ms Carroll added that the RTB now has increased powers to "investigate and sanction" cases of non-compliance with the Rent Pressure Zone measures.
She noted that their first investigations under the new powers have "officially commenced".
The RTB's latest figures show that during the April-June period (Q2) of 2019, the standardised national average rent was €1,202 per month.
That's up €79 compared to a year earlier.
Growth continues in Dublin, where the average rent of €1,713 represents a €114 (or 7.1%) jump compared to the previous year.
Rents are lower outside Dublin, but seven counties - Cork, Dublin, Galway, Kildare, Louth, Meath and Wicklow - have average rents exceeding or equaling €1,000 per month.