Academy principals have warned that their freedoms are "under threat", and have demanded reassurances from the main political parties that the next government will not water down their "hard-won" autonomy.
About 200 academy leaders have signed a letter addressed to the Conservatives, Liberal Democrats and Labour, calling for guarantees that their freedoms will be maintained.
The headteachers are concerned that their schools could face greater intervention from regional school commissioners (RSCs) - the eight officials appointed last year to monitor the performance of academies and free schools across England. Academy groups have also criticised proposals from both Labour and the Liberal Democrats that would prevent them from hiring unqualified teachers.
Last month, TES revealed that academies could be forced to sign over land to the government so that new schools can be built to tackle the shortage of pupil places.
This week's letter comes amid fresh warnings that the autonomy granted to academy leaders could be jeopardised by further changes brought in "under the radar". It has emerged that principals of schools converting to academy status will no longer automatically become a director of the academy trust that runs the school, which could severely reduce their influence.
The Freedom and Autonomy for Schools National Association (Fasna), which represents about 1,000 "self-governing" schools, said it was "alarmed" by the "loophole", and was seeking legal advice.
In the letter, almost 200 Fasna members demand to know if the political parties "will continue to support autonomy as a means of raising standards" in the country's schools.
According to Peter Beaven, chief executive designate of Fasna and a former head of an academy trust, the letter was prompted by mounting concerns that politicians could "restrict" academies' freedoms.
"We feel there might be a rolling back on the academy programme from what it was. For example, some of the things that academies and free schools can do [now] clearly won't be allowed under certain parties," he said.
"The policy that only qualified teachers can be used is one, and that local authorities may be employed to intervene in academies we feel is a model that has already been tried and found wanting."
Mr Beaven added that Fasna also had concerns that the RSCs - introduced to offer a so-called "middle tier" of oversight to the 5,000 academies and free schools in England - could become "over-burdensome" and begin "intervening in successful schools as well as those that are struggling".
Dame Kate Dethridge, headteacher of Churchend Primary Academy in Reading, said she shared concerns about the growing scrutiny of academies.
"Looking at the parties' policies, there is no guarantee that academies and free schools would continue to have autonomy," she said. "That doesn't mean schools shouldn't be accountable, but the amount of oversight should be in proportion to how successful you are."
These anxieties were shared by the Independent Academies Association (IAA), but the group said it was willing to wait and see what happened after the election. Its interim chief executive, Sir Peter Simpson, told TES: "We share their concerns that the autonomy enjoyed by academies is under threat but I'm not sure change is coming just yet."
In a recent survey, half of IAA members said they feared they would have fewer freedoms after the election, Sir Peter added.
The fears follow a change to the legal status of academy headteachers that was quietly introduced by the Department for Education at the end of last year. Under the "model articles of association" - which all schools must complete when converting to academy status - a headteacher is no longer guaranteed to be made a director of an academy trust when it converts. Although a headteacher (or executive headteacher, in the case of multi-academy trusts) can still be made a director, this must first be ratified by the board.
Alison Talbot, a partner at the law firm Blake Morgan, said the changes were "significant" and could deter schools from converting. "It's about being in control of the organisation," she told TES. "If a headteacher is not a trustee or director then they don't get to make any of the decisions over the strategic direction of the school, or how their budget is spent."
A DfE spokesperson said that the autonomy afforded to academy trusts meant they operated under a "strict system of oversight and accountability - more robust than in council-run schools".
"Academy trusts remain free to appoint headteachers as a trustee, but it is for members to approve this position," the spokesperson added. "This will ensure the most effective governance arrangements are in place."
`A change of policy may be destabilising'
Carl Ward, pictured, is chief executive of the City Learning Trust, a group of schools in Stoke-on-Trent.
According to Mr Ward, academy leaders are worried that a change in government would alter the "stability in the system".
"There's a general concern from an awful lot of headteachers that a Labour government may want to go back to a local authority-led system, which we think would be the wrong decision," Mr Ward says. "There have been general comments from Labour along those lines.
"We are at the early stages of a school-led improvement system and you have to unleash autonomy to allow that to work. My concern would be that a change of government and change of policy may destabilise that by giving more power back to local authorities."