The Revenue Commissioners have said there have been examples of "absolutely fraudulent behaviour" in relation to the Employment Wage Subsidy Scheme (EWSS).
Chairman Niall Cody said these cases have been referred to gardaí and in the context of the overall money paid out, they are very small.
However, he said Revenue was very concerned and these cases were "essentially robbery rather than tax evasion".
Mr Cody was speaking at a sitting of the Public Accounts Committee.
Fine Gael TD Alan Dillon asked why some many construction firms were still claiming EWSS although the sector was open.
Mr Cody said the scheme was calculated based on an annual drop in turnover.
He said €452 million was paid out under the EWSS in its highest month last July.
November saw payments of €321m.
In relation to the Temporary Wage Subsidy Scheme, which operated in 2020, Mr Cody said there had been "an exceptional level of compliance".