Hundreds of classroom assistants are hoping that intervention by the education minister will help them get their holiday pay.
Nipsa said those who work for the South Eastern Education and Library Board have been told that a mistake will delay the payment until September.
The assistants were not paid after an administrative error.
Most classroom assistants are usually only paid in term time, but get a lump sum for annual leave accrued in July.
The public sector union said they were on low pay and the holiday money is vital for the household expenses.
Alison Millar, the deputy general secretary, said an intervention by the education minister could bring a result.
"Within three quarters of an hour of making contact with the education minister's office, they had responded, indicating that they would take this up immediately with the south eastern board," she said.
"On Monday afternoon I was told that HR and payroll in the SEELB had received about 30 phone calls about this and Nipsa had received a dozen or more.
"Classroom assistants will be left severely disadvantaged over the summer."
No one from the SEELB was available for comment.