Some academy bosses are taking home "immoral" pay packets, a teaching union has heard, as it called for action to limit hefty salaries.
A small number of people are treating schools as a "gravy train", milking the taxpayer for as much as possible, the Association of Teachers and Lecturers' (ATL) annual conference was told.
Ministers need to set rules on chief executives' (CEO) pay, it was suggested.
Simon Clarkson, a delegate from Leicestershire, said: "Over the last two years things have got even worse.
"Executive headteachers have morphed, in a way that certainly has not been mighty, into CEOs, and the number of obscene salaries paid has increased.
"A small number of people have decided to treat education as a gravy train, and are milking schools, taxpayers and the funds that should be there for the children, for all they are worth.
"This has to stop. As well as being immoral, it is unsustainable.
"If it were sustainable, the older and more mature private sector market of independent schools would have fat cats in the way the academy and MAT (multi-academy trust) sector have now. They do not, and they do not for good reason.
"The excuses used for excessive CEO pay are myriad. Our response, however, should be simple. We should say no to any MAT CEO earning an excessive amount and certainly no to any CEO earning more than a local authority chief executive in the area where the headquarters of the MAT is based."
He added: "The system for setting the pay of MAT CEOs is wrong and this union needs to start lobbying for a change in that system now."
Seconding a motion calling for ATL to lobby government to ensure that the salaries and expenses of chief executives working in education trusts are not excessive, Tim Jefferson from Norfolk said that the position of CEO is an important role.
"When you look at the job description, the level of responsibility is clear," he said. "There's no doubt in this. The issue is with the amount of remuneration. Especially in the education context, and a lack of transparency in pay increases. This is, after all, taxpayers' money.
"Yes, being a CEO is a huge responsibility. Supporting students is a huge responsibility, teaching students is a huge responsibility, leading a school is a huge responsibility. There are no government rules, or guidance, on how this pay should be set. This needs to change."
Proposing the motion, Bob Groome from Norfolk highlighted a number of trusts, including Ormiston Academies Trust, whose outgoing chief executive Toby Salt, took home £ 205,001-£210,000 in 2015/16, up from £ 200,001-£205,000 in 2014/15.
The union passed the resolution with 98% of delegates in favour.
The debate comes after figures published in February showed that a number of academy bosses saw their salaries rise last year, with some taking home significantly more than the Prime Minister.
A Times Educational Supplement (TES) analysis of 20 academy trust accounts gave Sir Dan Moynihan, chief executive of the Harris Federation, as the highest individual earner.
He saw his pay packet rise from £395,000-£400,000 in 2014/15 to £420,000-£ 425,000.
A Harris Federation spokeswoman said at that time that the trust had transformed some of London's most challenging schools, and that its board " recognises that leadership is among the key drivers of our success, so leaders throughout our federation are rewarded for their contribution".
A Department for Education spokeswoman said: "It is for governing bodies to set school leaders' pay. We need the best people in our schools to help pupils reach their full potential which is why we have given all schools greater flexibility to set staff pay, reward exceptional leaders and attract strong leadership teams to work in the most challenging areas.
"This is in contrast to the old system which gave teachers pay rises simply for time served, regardless of whether or not they were doing a good job."