Following this week's revelations in this newspaper, Format Industrial Construction Ltd has given written guarantees that over 40 Polish construction workers in the port tunnel will now be paid the same as Irish workers.
But SIPTU construction official Eric Fleming said a letter circulated to all employees yesterday morning amounted to nothing less than an attempt at intimidation.
"I don't think they are going about this the right way. If the company is prepared to meet the conditions then there is no need for this. It's only going to make things worse," Mr Fleming said.
SIPTU's senior port tunnel steward John Rock said the letter, which the company warns will be treated as a sworn statement, had frightened employees. "It's like putting a gun to the head," he said.
In a statement, the port tunnel consortium, Nishimatsu Mowlem Irishenco (NMI), confirmed that Format president Wojciech Mikulecki had agreed to "comply in full with the National Working Rule Agreement and Irish labour legislation".
But Format's letter yesterday asked employees to answer 15 questions in an effort to uncover which workers had spoken to unions and the Irish Examiner about their conditions of employment.
The letter says Format is seeking to "undertake legal action and claim financial compensation from those who instigated such losses suffered by us. Accordingly, our intention is to find the source(s) of information used in press articles", it reads.
Although the letter promises that answering the company's questions will not result in any negative consequences for employees, it says Format "reserves the right to demand every employee to give true information and to enclose it as legal evidence".
The person responsible for ensuring all port tunnel construction companies are compliant, Paddy Hennessy of Contractors Administration Services (CAS), said it was unacceptable for Format to intimidate workers.
"If they are trying to intimidate the workers it would only make the situation worse. We made it quite clear that no worker would be intimidated over this," he said.
Although the NMI consortium was given a translation of the letter by the Irish Examiner, the group refused to comment until it had seen its own translation.
The Irish Examiner understands that NMI yesterday demanded that Format withdraw the letter immediately a demand that was met by Format.
Format declined to respond to messages seeking the company's comments.