The Financial Services Union has lodged a submission with the Competition and Consumer Protection Commission, outlining concerns it has with the proposed sale of the KBC performing loan book to Bank of Ireland.
Last month, KBC Bank Ireland announced that it is in discussions about the possible sale.
The deal, if coupled with a separate sale of its non-performing mortgage loan portfolio, would ultimately result in the bank's withdrawal from the Irish market.
John O'Connell, General Secretary of the FSU today informed staff of the submission to the CCPC at a virtual meeting which was attended by hundreds of KBC staff.
Mr O Connell said the submission outlined competition concerns and focused on what he said is a "lack of information" from KBC on the application of TUPE in any possible deal.
"Once again KBC staff have turned out in huge numbers voicing their frustration and concerns at the lack of information from KBC on their jobs and in particular on the application of TUPE legislation in any possible deal," Mr O'Connell said in a statement.
"KBC are still refusing to confirm that TUPE legislation, where staff follow the work, would apply to any deal between KBC and BOI and to negotiate formally with the FSU on industrial relation issues," he said.
Mr O'Connell added that the FSU has taken legal advice on the matter and have been informed that TUPE would apply to any such deal.
He said Bank of Ireland have also responded saying "where TUPE arise we will of course meet any obligations that arise. "