Fewer than one in 25 of those entitled to the expanded medical card have taken it up, the Dáil has heard.
Fine Gael TD Richard Bruton told the Dáil that the uptake stands at 3%, as it does for the new carers grant.
He noted that Revenue has reported that PAYE workers have failed to claim €480m in relief they are entitled to.
Deputy Bruton estimates that, on the expenditure side, the amount unclaimed stands at a further €1.5bln.
The unclaimed benefits are affecting vulnerable families the most, he said.
Tánaiste Micheál Martin said he would explore the suggestion that a cross-departmental group be established to tackle this.
