An agreement has still not been reached to enable schools for special needs children to reopen next Thursday, according to Fórsa.
The Department of Education wrote to principals last night to outline its plans for over 20,000 children to return to class that day.
It applies to special schools and children with special needs who attend mainstream primary school.
Minister for Education Norma Foley and Minister of State for Special Education and Inclusion Josepha Madigan said they had "positive engagement" with primary level and key education stakeholders yesterday.
Minister Foley said: “We are working together towards a phased return for children in special schools and a return to school for those in special classes in primary schools and children with significant additional needs in mainstream classes beginning on 21 January."
She added she is hopeful a pathway can be established for the return of all children to school at the start of February, "subject of course to Government and public health consideration".
However, the trade union Fórsa, which represents 12,000 special needs assistants (SNAs), said that efforts to reopen special schools and classes "were still underway".
In a statement, the union said an "agreement had yet to be reached on enhanced safety measures that would facilitate the safe resumption of services".
This is contingent on a number of measures including - DES obtaining new NPHET assessment of safety of staff and students attending school during this phase of the pandemic with the rationale and conclusions relayed directly to staff members.
— andy pike (@apike1) January 13, 2021
Fórsa said talks with the Department "had not concluded and that a number of issues remained to be resolved".
These include "the safety of SNAs at high risk of COVID infection" and the absence of childcare arrangements for workers.
It will not be confirmed until Tuesday whether special needs children can return to school next week.
In a further statement this afternoon, the Department of Education says an agreement was reached on the issuing of guidelines "which would support schools in making the necessary arrangements for the return of in-school teaching and learning for children with special educational needs in special schools and mainstream primary schools".
It said engagement will continue this week with the shared aim of resuming in-class learning this Thursday.
Speaking on Newstalk Breakfast with Susan Keogh, the General Secretary of the Irish National Teachers Organisation John Boyle said it was "unfortunate" and "not fair" that the letter to principals did not go out until 9pm last night.
He called for staff who work with children with special needs to be prioritised for the COVID-19 vaccine before classes resume.
"Before the schools would fully go back, what we're asking for at the moment is that reprioritisation would happen for those who work in intimate care being delivered to children with special educational needs," he said.
"Some of these children, unfortunately, it's much more difficult for them to keep a distance and the proper respiratory etiquette in a classroom.
'Cruel and disrespectful'
Furthermore, advocacy groups for children with special needs said they are "deeply concerned" at the lack of clarity about the reopening of special schools.
Four organisations, AsIAm, Down Syndrome Ireland, Family Carers Ireland and Inclusion Ireland, said it was "cruel and disrespectful" that thousands of children with additional needs could be given just 24 hours notice before a possible reopening.
A spokesperson said: "We have received calls and emails from many deeply upset and worried families today.
"Children with additional needs, and their parents, went to bed last night confident that the week ahead would see a much-needed return to the classroom and woke up this morning to mixed messages and deep confusion.
"It is vital the Department and stakeholders resolve outstanding issues over the weekend, that schools re-open next Thursday and that the needs of our children are front and centre in the consideration of all stakeholders moving forward."
This article was updated at 3.40pm
