NIPSA was last night blasted for its failure to give assurances that pupils with special needs will not be caught up in strike action.
In an interview with the Belfast Telegraph, chief executive of the Southern Education and Library Board Helen McClenaghan hit out after the public service union refused to say whether it will implement measures to ensure children with special needs can continue going to school during any industrial action by its members.
She said that according to legal advice, which she said has also been given to the unions in the dispute, the education and library boards cannot retain the 32.5 hour week but she stressed that classroom assistants will not lose any money.
But Nipsa's John Corey last night said the union had been told by its legal advisors that the retention of the 32.5 hour week is the contractual entitlement of all existing classroom assistants.
"The employers are claiming they have legal advice that says they can't apply the 32.5 hour week but that is contradictory to what we have been told," he said.
It has emerged one of the four unions involved in the dispute, the GMB, has voted in favour of accepting management's offer.
Mrs McClenaghan also said she was angry and frustrated that members of Nipsa are not being given the opportunity to express their opinion on the latest offer.
She said that, although the special needs allowance will be axed, classroom assistants will continue to receive the same amount of money in their pay.
Nipsa has said that it is determined to ensure the retention of the 32.5 hour week and the special needs allowance and recognition of NVQ level 3.
Up to 3,000 Nipsa members have already staged 10 days of walk outs and all out strike action was suspended a fortnight ago after it was agreed that negotiations should continue and include the Labour Relations Agency. But despite intensive talks, no deal was reached.
Mrs McClenaghan said the best possible outcome would be if classroom assistants who work with special needs pupils do not return to the picket line.
"These children need stability in their lives and I know the classroom assistants don't want to be out so I would urge them to get in touch with their employers to answer any queries they have about the offer," she said.