Health workers are considering taking legal action against a Stormont department after a payroll system failure meant hundreds will not be paid their correct wages again this month.
Health Minister Edwin Poots has been under fire for failing to tackle the long-running problem with the administration of staff salaries.
A union yesterday accused Mr Poots of being more interested in photo opportunities with health staff than paying them what they are owed.
Now workers in a number of trusts have been hit once again by what a union described as "the continuing saga of under payments, over payments, non payments and extra payments" triggered by "this flawed system".
It comes as public sector union Nipsa gathers today for its annual conference at the Slieve Donard Hotel, in Newcastle, Co Down.
Delegates will debate the payroll issue in a motion calling on the union to "pursue a case of maladministration in relation to the health minister's action in the imposition of this system".
Assistant secretary Kevin McCabe said: "These are the same HSC staff Mr Poots is so fond of lauding when he poses for photo-ops but who can no longer count on being paid correctly or even receive payslips to tell them of the errors caused in their pay in a timely manner."
Thousands of hospital workers across all trusts in Northern Ireland have been affected by incorrect payments. It started last October after a new payroll system was introduced.
A Department of Health spokesperson said: "The majority of staff affected have already had their tax code reviewed and amended, if required, by the HMRC. Following this review, the HMRC have confirmed that some staff will still remain on an emergency tax code, in line with normal business.
"Work is ongoing to ensure that this problem does not recur.
"A number of staff had incorrect deductions made in respect of their national insurance contributions. The cause has been identified and steps have been taken to ensure this problem does not recur. Payments have been made to staff to remedy any shortfall in payments."