Headteachers today faced calls to publish their salaries amid concerns that increasing numbers are earning six-figure sums.
Chief executives of other public sector organisations are required to make their wages public, and school leaders should not be exempt, according to Chris Keates, general secretary of the NASUWT teaching union.
She warned that as schools are given more freedoms, and rising numbers become academies, higher salaries are becoming more commonplace.
The union today passed a resolution at its annual conference in Glasgow calling on the executive to continue to campaign for greater transparency in the pay and rewards of school leaders.
"We have called for the publication of headteachers' salaries," Ms Keates said.
She added: "Why should they be exempt from chief executives in the public sector that have to have their salaries published?"
In one case, Ms Keates said, a school became an academy and the headteacher was then given a part-time contract.
"He was being paid the equivalent of what he was paid full time to be described as a consultant," she said, adding she understood he was earning around £100,000.
"That head had gone on to a three-day week, and another headteacher was taken on and described as the headteacher. That's clearly an abuse of public money."
And one academy in Staffordshire had put almost a third (32%) of its staff on the leadership pay scale, she said.
This means that they are all paid more than the highest-paid teacher at the school, and the minimum they could get is in excess of £45,000.
Delegates at the NASUWT's conference in Glasgow today were also told about a number of primary school teachers in the South West who were earning more money after calling themselves "executive heads".
"Just because they have changed their title, and they were in small primary schools, they were getting between £100,000 and £160,000," Ms Keates said.
She added: "We've heard of a number of these, headteachers taking schools through to academy conversion calling themselves executive heads and saying now they've got more responsibility they should get more pay.
"There's no rationale or debate about it."
Ms Keates warned that the Government is creating a culture in which schools do not have to stick to the national pay framework, and increasingly "anything goes", particularly for leadership pay.
Academies are free from the national pay framework, allowing them to set their own salary levels.
There is often no evidence for high pay levels, she said.
"Often its just on the nod rather than on production of rigorous evidence to identify why this is," she said.
"It's quite despicable," Ms Keates said, adding she was "absolutely convinced" that some of the motivation to go for academy status is pay.
"Some of the motivation to go is more flexibility on pay and terms of rewards for senior leaders."
The resolution raises concerns about the "disproportionate increases in leadership salaries as a result of the increased autonomy of schools which gives them greater control over their budgets".
It says that although abuse of the system is confined to a minority of governing bodies, "too many school leaders have secured inflated pay and benefits packages".
Last summer it emerged that one primary school head, Mark Elms, of Tidemill Primary School in south-east London, received a salary and benefits packages totalling £276,523 in 2009/10, including employers' pension.
Another head, Jacqui Valin, of Southfields Community College in south-west London, was handed a £20,594 (11.4%) pay rise to take her salary up to £198,406 in 2009/10.
Ministers have previously said they would consider proposals to cap headteachers' pay so that none would earn more than the Prime Minister, who receives around £142,500.