The NASUWT union has said that the Harris Federation, which runs 55 primary and secondary schools in London and Essex, is trying to make 45 teachers redundant.
Most of the job losses would be in south London, where around 11 schools could be impacted, they claim.
The Harris Federation has remained silent after being approached for comment.
According to the union, the trust, which has reserves of £21.5 million, has failed to provide a business case for the redundancies.
They also accuse academy boss Chief Executive Sir Dan Moynihan, who earns over £500,000 a year, of refusing to hold an academy-wide consultation on the proposed job losses.
NASUWT acting general secretary Matt Wrack said: “Harris Federation are trying to make dozens of dedicated teachers redundant and are using underhand tactics to try and force this through.
“Their disgraceful behaviour is causing untold stress to our members and will only serve to damage children’s education.
“This Academy Trust has tens of millions in the bank, pays its boss more than the Prime Minister and yet is seeking to get rid of 45 teachers in its schools.”
The union has now called on the academy trust to halt the planned redundancies, and to launch a “proper collective consultation” on its plans.
“NASUWT teachers are angry at this attack by their employer,” Mr Wrack added.
“They are united in their resolve and tell us that sacking teachers will only harm education provision and shatter already low morale across the trust.”
Schools Week has reported that a letter from the academy trust about the redundancies pointed to “unfunded” national pay rises for teachers as well as an increase in national insurance.
It also reportedly said that income is dropping as a result of falling pupil rolls, putting it in a “challenging situation”.
