Many of Northern Ireland's lowest paid health workers are still not getting the National Living Wage despite legislation being introduced in April.
The Department of Health had reassured 1,316 affected members of staff they would receive the pay increase plus arrears by July.
However, the department has yet to fully comply with the statutory requirement.
In a letter to an MLA, seen by the Press Association, health boss Richard Pengelly admitted "a delay" in fully implementing the pay requirement.
The Department of Health's permanent secretary said in the letter that a circular had been issued on March 22 advising that pay should be raised to £14,665 in line with the 2017 National Living Wage hourly rate for staff aged 25 and above, with effect from April.
But he admitted: "There has been an unfortunate delay in fully implementing the circular."
Mr Pengelly said he had been assured the majority of staff had received their increase plus arrears.
He added that HM Revenue & Customs, which enforces the legislation, is aware of the delays.
The National Living Wage was increased from £7.20 to £7.50 in April for those aged 25 and over.
The increase means a £500-a-year pay rise to full-time workers who do a 38-hour week.
SDLP MLA Patsy McGlone criticised the department for failing to comply with the statutory requirement.
He said those affected include domestic support workers, housekeeping assistants, drivers and nursery assistants.
"If it was pay lifts for directors and other senior members they wouldn't be having to wait this long. It is completely unacceptable to treat hard-working employees like this.
"We cannot expect a first-class health service here if some of the frontline staff delivering it continue to be paid less than the living wage.
"Many of those employed in Band 1 are already facing significant financial hardship and continued extremely low wages will only increase the pressure they are under. It is morally wrong."
The Department of Health has been asked to comment.