Schools that fail to tackle teachers' workload could lose control of their budgets and have their governing bodies replaced under tough plans being considered by the UK Government.
TES Cymru understands that ministers in Westminster intend to legislate to introduce the sanctions across England and Wales because little can be effectively done against schools that fail to act on the school workforce agreement.
The deal - signed by Government, unions and employers in 2003 - means teachers should have 10 per cent of their teaching time set aside for planning preparation and assessment, their cover for colleagues would be limited to no more than 38 hours during any school year, and they no longer have to carry out more than 20 admin and clerical tasks.
But teaching unions have been become increasingly concerned that many schools are not abiding by it.
Their fears were confirmed by a TES poll last month where 47 per cent of teachers said their school had not implemented the agreement in full.
Discussions between unions, employers and the Government this summer established that although local authorities have the power to remove governors' powers and replace them over financial irregularities, they cannot do the same where the agreement is broken - even though it is legally binding.
Teachers' pay and conditions, including the workforce agreement, are not a devolved matter to Wales and are governed by the UK Government's Department for Children, Schools and Families. Any decision on sanctions or enforcement action would be taken by the department.
An official announcement of the new penalties for errant schools is expected later this autumn.
A UK government source said: "Ministers really want to nail down these workload reforms and are concerned that employers are not delivering them - and we are working with the unions to toughen up existing legislation."
Geraint Davies, of NASUWT Cymru, backs the sanctions. "There are some headteachers who wrongly believe that the terms of the agreement are optional. They are not, but rather a legal responsibility for all schools," he said.
Mick Brookes, general secretary of the National Association of Head Teachers, said heads were "bending over backwards" to implement the deal, but some teachers wanted to continue with duties it had outlawed.
Phil Whitcombe, president of the Association of School and College Leaders Cymru and head of Bryn Hafren comprehensive at Barry in the Vale of Glamorgan, said he would be surprised if more than a "tiny number" of schools in Wales were not implementing the agreement. Those that were not were likely to be small schools in poor rural areas, he said.
Research in Wales has suggested that while the workforce agreement has reduced the burden for classroom teachers, it has actually increased it for senior staff in secondary schools.