The Education for Persons with Disabilities Bill "isn't worth the paper it is written on without a cast-iron guarantee of resources", the INTO has said.
Mr John Carr, general secretary of the union, has expressed dismay that the original Bill has been weakened substantially and is likely not to include children with specific learning disabilities such as dyslexia.
The original Bill committed the Minister to "providing such resources as are necessary" but it has been altered to "providing resources as are determined by the Minister".
The INTO is convinced that without a definition of disability in the Bill then children with disabilities such as dyslexia and conditions affecting behaviour and emotional development will not be included.
The INTO is also demanding increased staffing in the special needs section of the Department of Education and Science to support principals in their work. Meanwhile, the Catholic Secondary Schools Parents Association (CSSPA) has warned that inadequate resources mean that children with special needs are taking resources away from mainstream children.
"Most parents feel very, very strongly that if your child has no special needs your own child's resources will suffer," said Ms Barbara Johnston, PRO of the CSSPA.
"The Minister is mainstreaming everybody without putting in the resources so that they can cope," she said.
"The Minister is trying to make our schools one big melting pot. Mainstreaming more special needs kids will just make the situation worse." She said the most severe cases of disability were being catered for, while more common conditions, such as dyslexia and Asperger's Syndrome, were "being left in the cold".
The National Association of Principals and Deputy Principals has also expressed its concern that at second level children with special needs were not being given the resources they required, thereby placing pressure on the resources of entire schools.
Mr Carr said "primary schools want to be inclusive places where the needs of all children are met. But to do this effectively schools need resources for children with special educational needs.
"Principal teachers in all parts of the country know at first hand the difficulty in accessing resources for children with special needs." He said the bureaucracy surrounding applications for resources was creating overwork for principals. The huge administrative burden for principals, officials in the Department and psychologists was making it more difficult for principals to get information on resource applications.
"This leaves principals at school level trying to explain to parents why a badly-needed resource has not been put in place," he said.
The INTO wants to see each primary school getting a staffing quota of learning support teachers, resources teachers and special needs assistants based on the enrolment of the school in accordance with agreed criteria.
In the meantime, the INTO has demanded increased staffing levels in the special education section of the Department.