Drogheda in Co Louth and Greystones in Co Wicklow are being made rent pressure zones.
The towns have been added to the list of areas where landlords cannot raise prices by any more than 4% a year.
It comes as the average rents have gone up by 6.6% in the year to the end of June, according to new figures from the Residential Tenancies Board.
Average national rent in the second quarter of this year was €1,017 - up from €954 in the same period of 2016.
The latest stats also show that rents for Dublin apartments are now almost 15% higher than their previous record high in 2007.
Launching the RTB's report, Housing Minister Eoghan Murphy said there is anecdotal evidence that some landlords aren't complying with new rental rules, while some tenants are also willing to pay over the legal limits.
He said: "Measures like the RPZs take time to bed down. It takes time for people to understand them and for the changes in behaviour that they induce to become clear."
He added that modifications will be necessary, noting: "We don’t want to do something that may have a negative impact on the market, to the detriment of renters and landlords alike."
