Pupil Referral Unit (PRU) heads fear their schools will be taken over by private companies under a shake-up of education for excluded children.
An announcement on the future of PRUs - due to be renamed 'short stay schools' from September - is expected from the Government this month.
Jacky Mackenzie, secretary of the National Association of Short Stay Schools, is concerned that cuts to local authority budgets will lead to "private providers taking over our work to save money".
Speaking to The TES ahead of the association's annual conference, held in York last week, Mrs Mackenzie said: "We also want to know what impact the increase in the number of academies will have on us.
"Will this also mean an end to local authorities running PRUs - particularly if they are not running so many local schools?"
Education Secretary Michael Gove has promised headteachers more powers to exclude, and has previously said he wants to abolish appeals panels. He has also pledged "improved provision for excluded pupils to get their lives back on track" but has not made the role of PRUs clear.
The previous government was also in favour of outside involvement in running PRUs, but so far this has only included charities. Around 12 pilot projects are running around the country.
"People who don't understand our work still think we are 'sin-bins', they don't see the way we turn lives around or our strong partnerships with schools," Mrs Mackenzie said.
From September 1 all short stay schools will have to form a partnership with a local primary or secondary.
The National Organisation for Short Stay Schools will also lobby the Government this year about the new Ofsted framework. It is concerned that it penalises PRUs because of the new focus on academic results.