Two landlords have received criminal convictions and more than €7,000 in fines for failing to register their rental properties.
One of the houses was in Mullingar, Co Westmeath while the other property was in Tallaght in Dublin.
The Private Residential Tenancies Board (PRTB) said both landlords had previously received a number of statutory notices and warning letters instructing them to make sure they were on the register.
Section 134 of the Residential Tenancies Act 2004 requires the PRTB to pursue landlords for failing to register their tenancies.
The agency sent 22,854 letters in 2015 notifying landlords of their specific registration requirement.
The fee is €90.00 per tenancy if registered within one month of the tenancy commencing. A late fee of €180.00 applies if the tenancy is registered outside of that time period.
If convicted of failing to register a property, a landlord faces a fine of up to €4,000 and/or six months imprisonment, along with a daily fine of €250 for a continuing offence, ie where the tenancy continues to remain unregistered after the court hearing.
One in five homes in Ireland is rented, including more than 100,000 households who are supported by State-supported schemes such as rent supplement, the housing assistance programme or the rental accommodation scheme.