More than 6,200 partners are not paying child maintenance to the other parent, authorities say.
Figures obtained by The Irish Times show inspectors in the Department of Social and Family Affairs have identified more than 8,000 spouses or partners who should be paying maintenance. However, just 1,779 of these parents are doing so.
The Minister for Social and Family Affairs, Mr Brennan, has warned that court cases were pending against anyone who refused to pay child maintenance.
The Department has initiated more than 150 court actions against these parents in recent years.
Mr Brennan is reviewing aspects of the maintenance recovery system and is to analyse how other European countries operate similar schemes, in a bid to modernise the social welfare system here.
The cost of one-parent family payments to the State is substantial, at around €700 million a year.
While just a fraction of liable parents are paying child maintenance, there have been significant improvements in tracking down those who have refused to meet their legal obligations.
This approach resulted in savings of €14 million last year through liable parents paying child maintenance and the consequent reduction in State-funded one-parent family payments. This compares to savings of just €2 million in 2001.
However, many of the non-paying parents who have been tracked down are not obliged to contribute because they are on social welfare or low incomes.
The Department assesses the ability of the person to pay based on a number of factors, including the liable parent's net income and mortgage re-payment obligations.
The system of recovering child maintenance was overhauled some years ago when staffing levels in the relevant area were almost doubled and the approach towards recovering maintenance was streamlined.
In order to encourage lone parents to seek maintenance payments from the other parents, claimants have been allowed to retain half of any maintenance they receive without a reduction in their social welfare entitlements since 2001.