The large discrepancy between the number of people signing on the Live Register and those recorded as unemployed is to be examined by the Dail Public Accounts Committee (PAC), according to its chairman, Fine Gael TD Mr Jim Mitchell.
The results will show the extent to which the State is being ripped off by people working in the black economy, he said.
The PAC has directed the Department of Social, Community and Family Affairs to carry out pilot projects in Galway and Waterford to examine the numbers of jobs available, but unfilled, compared to the number of people who are unemployed and claiming social welfare.
These results will be used as a baseline for the committee for other regions when it begins its wider examinations, Mr Mitchell said.
"Through this detailed examination we will get a more thorough picture of whether we are being ripped off or not.
"We will get a much more forensic view of the situation on the ground.
"If all the worst assumptions are realised this could be very big and comparable to the DIRT inquiry," Mr Mitchell said.
He also said the committee might seek Dail approval for an investigation into the construction industry, similar to the inquiry into banks and DIRT.
Mr Mitchell said that according to the Live Register 143,000 people were claiming unemployment payments each week, of whom 120,000 under 65 years old were getting full unemployment payments or their equivalent.
"Yet we are then told by the quarterly Labour Force Survey that there are only 81,000 unemployed and it is accepted uncritically.
"Why are we paying 39,000 full unemployment payments if these people are not fully unemployed? That is the minimum gap and it could be much bigger. "Many of these are making bogus claims. They almost certainly have other earnings and are almost certainly claiming secondary benefits for themselves and partners through rental and mortgage subsidies and medical cards," he said.
When they reached retirement age, he added, these people would be drawing non-contributory pensions, having not contributed to the State through PAYE and PRSI contributions.
Representatives from the Galway Chamber of Commerce recently told the committee they had 2,500 vacancies which their members could not fill, yet there were 2,300 people registered as long-term unemployed. As a result of this the committee asked the Department of Social, Community and Family Affairs to carry out a detailed examination of the situation there. In September a similar "forensic examination" will begin in Waterford.
Referring to the building industry, Mr Mitchell said it was reasonable to assume that some of the discrepancy in the figures there could be accounted for by the phenomenon of subcontracting. The PAC wanted to examine whether, and to what extent, subcontractors in this sector were claiming unemployment benefits.
The committee is waiting on detailed papers from various Government departments and other groups such a trade unions and the Construction Industry Federation for a "more thorough picture of the situation".