The receiver at waste recovery firm Greenstar has told the company's 550 employees that they have until Friday to accept significant pay cuts or face the possible liquidation of the firm.
David Carson of Deloitte has previously told unions that there was a possibility of finding a buyer of the company, but that the cost base, including wages, was too high.
David Lane of SIPTU said the receiver had told staff that they would have to accept wage reductions of up to 38% to make the company viable.
He said it was unlikely that that the union could reach a deal, as the proposed cuts were "too severe".
Employees have already been told that even if the company is sold, there will be redundancies and that staff will only get statutory redundancy.
Mr Lane also said the receiver has asked for expressions of interest in redundancy to be sent to him by Friday.
A spokesperson for Deloitte declined to comment.
The receiver is due to meet unions tomorrow in Portlaoise.