The organisation received over 130,000 calls last year
The Residential Tenancies Board (RTB) says 2016 was its busiest year to date.
The organisation says it received over 130,000 calls - an increase of 10% from 2015 - and more than 51,000 e-mail queries (up 5.5%).
The RTB noted considerable changes have taken place since last year, with 55% of tenancies now covered by Rent Pressure Zones.
Since they were introduced, the number of calls per day to the RTB has increased from 600 a day to 1,000 at its peak.
While the number of dispute applications about rent reviews has increased by 160% in the eight month period.
Rosalind Carroll, RTB director said: "We would encourage any existing or new tenants who are faced with increases over and above 4% or to refer a dispute to the RTB, as well as tenants renting a new property.
"Even if a tenant has agreed to a rent and signed a tenancy agreement, they are still protected under the law; they cannot contract out their rights.
"If a landlord has been found to have charged an illegitimate rent, it has significant consequences and damages up to €20,000 can be awarded as well as repayment of the additional rent."
At the end of the year, there were 325,372 registered tenancies, 6,000 more than in 2015.
Its annual report says over 106,000 new tenancies were registered in 2016, compared with 111,000 in 2013, which it says suggests that many households are staying longer in their tenancies as supply remains constrained.
The number of registered landlords remained steady at 175,000 at the end of 2016, and over 70% of those had just one property registered.
Last year, the RTB received 4,837 new applications for dispute resolution.
While this was a 20% increase on 2015, it says it was in line with the increase in overall tenancies in the sector.
The most common dispute types remained rent arrears and over-holding by tenants, and invalid notice of termination and deposit retention by landlords.
The RTB has also focused on ongoing improvement in case processing times - reducing from 14 weeks in 2015 to 12 weeks in 2016.