Children with special educational needs could lose out in England's academies expansion, council managers warn.
Vital services could become unviable if large numbers of schools become academies, directors of children's services say.
Councils currently keep 10% of school budgets to provide services, including help for pupils with special needs.
But the government says its policies will allow head teachers to give the best support.
Academies have a duty to provide support for pupils with special educational needs as part of their grant contract.
Schools which break away from local authorities will be directly funded by the government and will have more freedom over their budgets, curriculum and admissions.
They are free to buy in specialist services - from councils or other sources.
'Burden of regulation'
The Association of Directors of Children's Services has written to the new Education Secretary Michael Gove to set out priorities and how it believes it can work with the government to "achieve shared aspirations for improving the lives of children in England".
The directors say they believe they can play a "significant role" in achieving the new government's "stated policy objectives".
In the letter, they welcome some of the changes being introduced by the government - such as moves to reform the inspection system and "lift the burden of regulation on schools and local government".
But they highlight the value of services they provide to schools, parents and young people.
They say they want to work with the government "to ensure that inevitable changes to the way schools and local authorities are funded... do not have the unintended consequence of rendering valued support services unviable".
The president of the Association of Director's of Children's Services, Marion Davis, said services could be maintained at current levels only if academies chose to buy them from councils.
She told the Times Educational Supplement: "If a significant number of schools convert to academies, there's a real risk that it makes some services that local authorities provide unviable. That's the big risk.
"These are people with qualifications and experience and they are not necessarily the cheapest of staff. If those budgets go, there is the danger of having to cut right back on specialist staff that make a vital difference to children's outcomes."
At a recent news conference where he officially launched the academies programme, Mr Gove said academy heads would be free to innovate and choose the best support for children with special educational needs.
And many special schools were themselves opting to become academies.
A spokesman for the Department for Education said funding for pupils with special educational needs followed the individual, so no child would miss out.
"Academies have the freedom to select the support which is most suited to their pupils - sometimes by buying in new, better support and provision, or sometimes using existing local authority services if they are strong," he said.
"Ultimately we trust teachers to know what's best for their pupils."