Hundreds of deaf and blind children have had their access to specialised support severely restricted since the start of the school year.
This is because the Department of Education and Science has not yet replaced trained visiting teachers who have retired.
In a move which has caused frustration among parents of children with hearing and visual impairments, it is understood that the Department has so far failed to replace six visiting teachers in Galway, Mayo, Waterford, Wicklow, Cavan and Monaghan.
While some members of the visiting teachers service (VTS) have taken on extra caseloads in order to ensure students are continuing to receive the service, this is no longer the case following a letter from the Irish National Teachers' Organisation (INTO) to its members on the matter.
In the letter, Mr John Carr, the general secretary of the union, writes that, although it had asked the Department to carry out a review of the future role and development of the VTS, it was "unacceptable" that the posts remain unfilled.
"The INTO is therefore advising members of the service not to engage in work which should, by right, be done by a person appointed to one of the existing vacant posts, pending the outcome of negotiations with DES," he states.
The 41-strong VTS provides support to children with hearing or visual impairments and their families, from diagnosis until they complete full-time education.
Visiting teachers work with children in the home at pre-school stage, to develop language or visual ability, and continue to work with teachers in mainstream schools to facilitate the inclusion of the child.
Ms Mary Quinlan, joint chair of VISTA, the professional body for visiting teachers, said the failure by the Department to replace the visiting teachers had created an "awful situation" for the children concerned.
While individual caseloads varied, she estimated that most visiting teachers dealt with between 50 and 60 cases.
Much of this would involve working with pre-school children and supporting parents when diagnosed, she said.
Five of the six unfilled posts are understood to be for teachers of the deaf.