Polish firm Format Industrial Construction Ltd made written commitments to pay workers properly in February following an extensive Irish Examiner investigation.
At the time, up to 40 Polish Port Tunnel workers were being paid just over e8 an hour instead of the agreed industry standard of over €15.
The workers did not receive holiday pay or overtime payments, although flights home and accommodation were provided.
Although some improvements have been made, frustrated unions and Port Tunnel management are still not satisfied that proper pay arrangements have been put in place.
At a lengthy meeting yesterday between Format, Port Tunnel operators Mowlems and SIPTU, officials complained that new underpaid Format workers on two other Dublin building sites have also been discovered.
And with the absence of satisfactory pay slips, SIPTU also said Format - which is the subject of a continuing investigation by the Labour Inspectorate - was continuing to breach pay agreements.
"They still haven't complied with the pay agreements here. And we're not happy that the company are repeating this on other sites throughout the city," said SIPTU's construction branch secretary Eric Fleming.
Senior sources in Mowlems - which has threatened to throw Format off the tunnel job and take on the workers itself - also said they were extremely frustrated with Format's approach.
"They are resisting this all the way. But it has to happen. Either they comply or they go," he said.
Contacted by the Irish Examiner last night, Format's Irish representative Edwin Aviles hung up, before turning off his phone.
Meanwhile, as the Irish Congress of Trade Unions (ICTU) yesterday called for tough new regulations to combat the exploitation of migrant workers, Tánaiste Mary Harney continued to reject accusations that she did not act to prevent abuses at Turkish firm Gama.
Following two weeks of unprecedented protests by hundreds of Gama workers, Ms Harney said she would condemn discrimination against any workers.
On Monday, the Government will argue before the High Court that it is in the public interest for a Labour Inspectorate report into allegations of wage fraud and underpayment at Gama to be published.
Gama, despite initially welcoming the Labour Inspectorate investigation, has taken out two separate injunctions preventing publication of the report.