Ulster University (UU) has apologised for failing to pay more than £1m in compensation to 143 former employees by an agreed date.
The former staff are each due to receive 90 days worth of salary after an industrial tribunal judgement.
But in an email to some of the affected staff, seen by the BBC, UU said payment was "taking longer than we had anticipated".
The University and College Union (UCU) has criticised the delay.
Some of the affected former staff received an email from a UU finance official on Tuesday.
"The university had intended to make the payment due to you by 15 January," it said.
"Please accept my apologies for the delay.
"Because of the nature of the award this is taking longer than we had anticipated and we hope to have all payments completed over the next few days."
The email's author said they could not be more specific about a date but payment would be processed "as soon as possible".
'Adding insult to injury'
The UCU said that the delay could leave the university facing an additional bill.
The union, which represents many of the university's staff, said that 8% interest a day was due on each payment for every day beyond 15 January.
Tracy Irwin, the UCU president at the university, said it had not given the staff an explanation for the delay.
"This lack of payment really adds insult to the injury our members have suffered," she said.
"We call on management to rectify the situation as a matter of urgency and to apologise to the dismissed colleagues for the further stress this delay has caused."
UU was unable to specify how many of the 143 former staff had not received the agreed compensation.
In a statement, the university said the delay was due to "technical, calculation and statutory requirements".
"We have apologised for this delay directly to those involved and have reassured them the remaining payments will be made as soon as possible," said UU.
In December 2017, an industrial tribunal ruled that the university was guilty of a "serious failure to consult" with the UCU over the redundancy process for the 143 staff in April 2016.