Academy Enterprise Trust wants for-profit body to take over non-teaching posts such as librarians and secretaries

The largest academy chain in the country is seeking to outsource all non-teaching posts in its 77 schools, from librarians to caretakers, to a for-profit organisation within the next month.

In a step that critics fear is a major step to putting profit-making at the heart of the state school system, the Academy Enterprise Trust has selected PricewaterhouseCoopers (PwC), one of the world's largest auditors, with a specialism in tax accountancy, as a partner in the plan.

The controversial proposal, which AET admits is entirely new to academy trusts, is being reviewed by the government. AET wants to set up a limited liability partnership with PwC, which would be paid up to £400m of taxpayers' money over 10 years for its role.

The new organisation, created by the partnership with AET, would take over responsibility for providing school business managers, IT staff, secretarial staff, and finanicial expertise, along with speech and language therapy provision, education psychology, education welfare, curriculum development and professional development. PwC does not have a background in such services, so it is expected that it would subcontract to other private firms and mainly manage the budgets.

The move has caused outrage among staff. The public sector union Unison, which believes that more than 500 of its members would be affected, fears that each private firm involved in the provision of services would be taking a slice of the public money paid to schools.

A letter sent to staff a week ago by Ian Comfort, chief executive of AET, said that it expected the government's Education Funding Agency to report back on the proposal over the next month.

Comfort added that PwC "has agreed to work with us at no cost to assist us in reviewing our services to ensure that they are efficient and effective".

Oliver Coppard, a vice-chair of governors at an AET academy, Firth Park in Sheffield, is planning to stand against deputy prime minister Nick Clegg in the 2015 general election in protest at the move. Coppard, a Labour candidate, said: "We had a meeting of the staff who are going to be affected in the school and, of course, they are really concerned. I believe this is a step towards the privatising of our schools by stealth"

Unison's head of education, Jon Richards, said he believed that there were concerns even within the Department for Education at the move, despite the new education secretary Nicky Morgan's recent suggestion that she was open to free schools operating for a profit in the future.

He said: "This move to effectively remove the control of most of the school from headteachers and, we believe, to potentially put profits before pupils is a dangerous decision, and we are urging AET to stop this privatisation process."

AET, which has been criticised for its poor performance in managing schools, was discovered last year to have paid nearly £500,000 over three years into the private business interests of its trustees and executives. The payments were for services ranging from project management to HR consultancy, according to the academy chain's company accounts.

A spokesman for AET said that they had a duty to demonstrate value for money in the use of public funds. He said: "As an exempt charity, accountable to both the secretary of state and the Charity Commission, we have a commitment to maintaining the quality of school services, and we reinvest all surpluses into the running of our schools.

"In December 2013, the AET board therefore agreed to issue a tender to seek expressions of interest from organisations who may be able to work with us to provide more efficient, effective and economic services. Our aim is to seek a partner that will bring additional expertise, experience and capital to strengthen our operations.

"We received a number of responses and following a lengthy tendering process, PwC was identified as the partner that had made the strongest bid.

"The proposed changes would not impact on the ability of headteachers to run their schools. All staff working at AET academies would continue to work under the direction of the headteacher."

A spokesman for the Department for Education said: "It is for the board of AET's trust to decide how they provide effective services for their schools, providing it is in line with their funding agreement.

"It is right that any proposal of this scale is then subjected to further scrutiny to ensure it provides the best value for the taxpayer and it can only be implemented after approval by the secretary of state."