The number of on-site inspections carried out by the Revenue Commissioners fell dramatically in 2020 due to the Covid-19 pandemic, according to chairman Niall Cody.
In correspondence sent to the Oireachtas Public Accounts Committee, Mr Cody confirmed that last year, they carried out just 360 construction site visits - down from 1,673 in 2019 and 1,471 in 2018.
For years, unions have voiced concerns about developments in construction, where many workers are forced to operate as self-employed contractors rather than direct employees in order to secure work.
The arrangement - described as "bogus" or "false" employment - benefits employers because they pay less PRSI, but it can leave workers losing out on social welfare entitlements that accrue to employees.
Critics also argue that such arrangements result in lost PRSI revenue for the state, with estimates running to hundreds of millions of euro.
The Revenue chairman confirmed that a further 1,076 site visits were undertaken across a range of business sectors in 2020, including restaurants, pubs, takeaways, nail bars, boutiques, scrap metal dealers, architects, taxi operators, and IT service operators.
Again, the overall number of visits was down compared to 2019 with 4,091 inspections, and 2018 when 2,758 were carried out. Mr Cody said they did not maintain statistics relating to the number of specific visits to each individual sector.
The Revenue head was unable to give an estimate for the rate of bogus self-employment in Ireland, or an estimate of its cost to the exchequer.
He described bogus self-employment as "complex, varying case by case and not, due to its nature reported to Revenue or any other agency". As a result, it was not possible to accurately estimate the overall scale of such activity.
He said the actual losses to the state would differ depending on the particular circumstances of individual cases.
He noted that a 2018 report had made certain observations relating to the differential between social insurance rates for the employed and the self-employed, but said that was a policy matter outside Revenue's remit.
He confirmed that all couriers are deemed self-employed for PRSI purposes - even if they work for just one employer - due to a previous Social Welfare Appeals Officer's decision.
"In the interest of uniformity Revenue decided, without prejudice, to treat those couriers as self-employed for tax purposes," he said.
Mr Cody confirmed that the Revenue have stopped data access requests to telecommunication companies on the advice of the Attorney General's office following a number of court rulings.
There were 40 such requests in 2017and 26 in 2018.
He said Revenue continued to investigate all forms of serious tax and duty offences.