The Central Bank has released new figures showing that 11.3pc of private residential mortgages are three months behind.
At the end of September there were 86,146 in serious trouble compared to 81,035 or 10.6pc at the end of June 2012.
This figure includes 67,401 mortgages in arrears of more than 180 days.
Fianna Fail's Michael McGrath said: "The figures released by the Central Bank show that almost one in four family home mortgages are either in arrears or have already been restructured.
"This confirms Fianna Fail's view that the introduction of a property tax at this time is a major mistake."
More than 180,000 mortgage holders are experiencing difficulty in repaying the mortgage on the family home at this time, he said.
"The figures released today also confirm for the first time that 34pc of buy-to-let mortgages are now in arrears or have been restructured," said Mr McGrath.
"Many of these landlords will inevitably end up in the insolvency regime. The introduction of a property tax will result in a lot of landlords getting out of the business with the inevitable consequence of rents increasing further."
On the eve of the Government introducing the property tax bill in the Dail, Fianna Fail was again calling on the Government to abandon this plan.
"This property tax will push many ordinary families over the edge and should be abandoned before it is too late, "Mr McGrath said.
The Central Bank, in its report, noted that the rate at which arrears figures are increasing is slowing down.
The figures also indicated that 26,770 or 17.9pc of buy-to-let properties were in arrears of more than 90 days at the end of September, an increase of nearly 2,000 from the last quarter.
Lenders took possession of 154 properties during the third quarter, of which 47 were repossessed on foot of a court order while 107 were voluntarily surrendered or abandoned.
David Hall, from the Irish Mortgage Holders Organisation, said the mortgage crisis is now fully out of control, due to years of Government inaction.
"The facts show that there are 65,000 homes in arrears of 180 to 720 days. This is a startling statistic," he said.
A generation of Irish people "is now locked into an endless battle of attrition with the banks", Mr Hall added.
The organisation believes that while the introduction of the Insolvency Bill will provide a formal framework for the resolution of debts, it is fundamentally flawed.
The New Beginning group warned that the latest mortgage arrears figures from the Central Bank revealed an intensifying economic crisis. New Beginning's Ross Maguire said that any notion that numbers are lessening fails to look at the reality. "Over 700,000 people are directly affected by this problem today," he said.