New caps on headteacher pay need to be introduced to end a growing bonus culture for state school leaders, the TUC conference has declared.
Schools should also have a legal duty to publish the pay and rewards given to heads each year, according to a motion passed at the conference in Liverpool.
Some have been "seduced" into seeing headship as a way to make money, according to Mary Bousted, general secretary of the Association of Teachers and Lecturers, which proposed the motion.
The result is that money is being diverted away from children's education, she warned. "We do not want a generation of school leaders who think the bottom line has a pound sign instead of being about public service," said Dr Bousted.
Chris Keates, general secretary of the NASUWT, said school leaders' pay should be published to bring it into line with other senior public service jobs.
"Too many people forget that school funds are taxpayers' money," she said. "Publishing pay would make the position of headteachers consistent with other public servants in chief executive roles."
The calls for new rules come after The TES revealed last week that heads are earning up to pound;50,000 a year on top of their regular pay for advising struggling state schools on ways to improve.
Successful heads are charging up to pound;850 a day for their expertise. A number have struck deals with their governing bodies allowing them to split their profits with their home schools.
In April, Hank Roberts, a union representative, claimed that around pound;1 million had been paid in bonuses over the past seven years to the senior management team at Copland Community School in Brent, north London.
Copland's former chair of governors confirmed that the school's headteacher, Sir Alan Davies, was paid a bonus of pound;50,000 two years ago and pound;80,000 last year.
Sir Alan, the deputy headteacher and the school's bursar have been suspended by Brent Council spending the result of an ongoing investigation.
Schools Secretary Ed Balls subsequently sacked Copland's governors, but he has expressed reservations about limiting the pay of executive heads who run more than one school.
Speaking at an ATL fringe meeting at the TUC, Dr Bousted said: "The vast majority of school leaders in England and Wales still see education as a public service, but a few have been seduced into seeing it as a chance to make money.
"We strongly support schools working together to share good practice, and we strongly support school leaders working together.
"But we do not support the growth in executive heads, consultant heads, superheads, and super-duper heads.
"Let's not forget that every pound of bonus paid above the school leadership pay scale is a pound less for books and equipment for pupils, and less for classroom based staff."
John Dunford, general secretary of the Association of School and College Leaders, agreed that pay arrangements for heads should be transparent and publicly available.
But he added: "Any connection between additional payments for headteachers taking on additional responsibilities in support of other schools is completely different from bonuses for bankers. It is completely wrong for the TUC to imply that there is any similarity."