One of the unions representing classroom assistants has criticised the decision by Nipsa to hold a one-day strike on Wednesday.
Unions plan further strike action next week
The four unions and employers are resuming talks held on Tuesday, where there were signs of progress.
GMB union spokesman Eamonn Coy said: "I cannot understand why any union would go on strike in circumstances where negotiations are ongoing."
Nipsa's John Corey described Mr Coy's comments as "disgraceful".
"They do a disservice to the thousands of classroom assistants who took strike action on Wednesday and gave full and unequivocal support for that," he said.
However, Mr Coy said he believed the dispute could be resolved without members of his union taking strike action.
"I will not have GMB members unnecessarily lose pay, they are already on low pay," he said.
If the dispute is not settled, Nipsa has warned that a further three-day strike could take place next week, followed by an all-out strike the following week.