A glitch-hit payment system for hospital staff which led to thousands of workers across Northern Ireland being underpaid by over £400,000 has been branded "totally unacceptable" by unions.
The heavy criticism was made by Unison and the Royal College of Nursing after the health trusts confirmed that staff – believed to be mostly nurses – had received incorrect payments.
Technical difficulties with the new system have been blamed for the payroll problem, that is understood to have been ongoing for at least three months.
Within the past seven days the Belfast Trust confirmed approximately 1,200 employees of the 4,383 weekly paid staff were underpaid.
The South Eastern Health Trust said that over three months it had made a total of £426,000 of additional payments. But a spokeswoman said this was "against a three-monthly pay bill of over £80m, for 13,000 posts".
The Southern Trust confirmed it will pay £12,000 next week to staff after a "system error" in March salaries.
In the Northern Trust it said it expected to make 68 additional payments to staff arising from underpayments of salary in March 2014.
The Western Trust did not provide a number of staff effected.
A spokeswoman for the trust said: "A small number of Western Health and Social Care Trust staff have experienced a delay in receiving payments for enhancements and overtime.
"Basic salary was paid on pay day to all staff."
All trusts said they were taking action to address the situation.
Unison said employers had been warned on a number of occasions that incorrect salary payments and delays were occuring.
Anne Speed, lead negotiator on Health for Unison Northern Ireland, said: "Current systems are intolerable and totally unacceptable and those responsible should take immediate steps to correct."
Janice Smyth, director of the Royal College of Nursing in Northern Ireland, said staff had been let down. "The measures put in place and the response shows an absolute lack of respect or any understanding," she said.
A spokeswoman for the Belfast Trust said it has a dedicated payroll helpline for queries and have been holding drop-in clinics across the sites to "ensure solutions are agreed quickly".
A spokeswoman for the South Eastern Health Trust said: "We are doing all we can to minimise impact on staff."
A spokeswoman for the Southern Trust said it has been able to correct the problem quickly.
Thousands of hospital workers across all the Northern Ireland Health Trusts have been affected by underpayment. It started three months ago following the implementation of the new payroll system. The trusts have apologised to workers and have said measures have been put in place to address the problems. But unions remain angry at the response.