The Government is seeking the return of almost €34m which was wrongly claimed in Pandemic Unemployment Payments (PUP) at the height of the Covid-19 outbreak.
The Department of Social Protection told RTÉ's This Week programme that, up to the end of July, just over 18,700 Pandemic Unemployment Payment over-payments were recorded to a value of €46.5m.
In total some €12.6m has been repaid, with approximately 10,700 of these over-payments having been repaid in full.
However some €33.9m has still not been paid back.
The Department said it continues to make efforts to recover all outstanding over-payments.
Over-payments can happen for a variety of reasons, including claimants failing to notify the Department of Social Protection when they returned to work.
However in some cases, the Department has detected fraudulent claims of the Pandemic Unemployment Payment.
A team of 120 officers, including 20 gardaí and one sergeant, have been tasked with investigating and detecting social welfare fraud.
In a statement the Department said: "Where we find suspected fraudulent claiming, we pursue those who offend to ensure the funds are returned and the most severe cases are brought to the attention of the Courts."
"Cases suitable for prosecution are identified during the course of investigations conducted primarily by the Department's Special Investigation Unit and gardaí seconded to the Special Investigation Unit."
The Department said it has several ongoing prosecutions going through the courts system currently, and to date four PUP cases have been finalised with convictions secured in each case.