Hundreds of nurses have had to pay money back to the NHS despite receiving a pay rise.
The Department of Health (DoH) implemented a pay award for Health and Social Care (HSC) employees last month.
But the pay rise has resulted in 787 workers – 1.1% of HSC staff – taking home less money as it put them in a higher pension bracket.
The DoH said there had been “significant communication” with staff and trade unions on the issue.
“It’s grossly unfair. We didn’t fight this long for a pay rise to end up being out of pocket,” a nurse told BBC News NI.
“It makes you feel so undervalued, like nobody really cares at all.
“The pressure on staff is in the health care system in Northern Ireland is ridiculous at the minute yet here we are with even less money at the end of the month.”
The nurse faces a salary deduction of £240 this month.
“I worked all over Christmas, hardly saw my family or friends, and I work long hours, trying to do my job the best I can for the patients and now I’m hit with a bill for £240 to be taken from my salary this month. How is that fair?”
“It’s hard enough to attract people to nursing because of how much pressure staff are under and this could well push good nurses away completely.”
Rita Devlin, acting deputy director of the Royal College of Nursing (RCN) in Northern Ireland, said the pay deal was not agreed by the trade union.
She said the RCN’s concerns had been raised with the Department of Health.
“We already have a high vacancy rate in Northern Ireland with nearly 2,000 posts in the HSC alone unfilled,” Ms Devlin told BBC News NI.
“We can ill afford to lose any more of our highly trained nurses. We would urge the DoH to ensure that we are not in the same position this time next year.”
A spokesperson for the DoH said: “There was significant communication directly with staff and with trade unions on this issue.
“Mitigation arrangements have been made available for any staff member whose backdated pay increase does not cover backdated pension contribution arrears. Any such deficit can be paid through wage deductions over a period of up to 12 months.”
The department states that there are seven different contribution rates, based on seven earnings brackets, meaning that “the more a staff member earns, the higher their contribution rate may be”.