More inspections of school building sites by Revenue are to take place this summer to check if undeclared workers have been hired to complete large Government contracts.
An ongoing investigation by the Department of Education has so far found problems around record keeping and shortfalls in workers' pay.
The Government will spend €475m building and repairing schools this year.
But there have been repeated reports that some workers building these schools are not registered.
That means they may not have paid tax or social insurance.
Last year a site inspection in the southern region where dozens of people were interviewed appeared to verify these reports, according to documents circulated between Revenue and the Department of Social Protection.
Questions were also raised about the ability of some school boards of management to handle certain VAT charges.
The documents, released to RTÉ News under the Freedom of Information Act, say the Department of Education's own efforts to deal with the problems have so far uncovered minor problems.
The department said the private firm it hired to inspect these sites has passed on information to Revenue and Social Protection.
It has also tackled shortfalls in workers' pay and its work complements that of Revenue and Social Protection, a spokesperson said.
Another initiative has seen a school building in west Dublin monitored by the department's compliance firm throughout its construction.
However, Revenue has confirmed it will still inspect several sites during the school holidays.