Parents across Powys have been urged by head teachers to protest about a possible 2% cut in next year's education budget.
Heads fear that class sizes will increase after budget cuts
In an unprecedented step, the heads of every primary and secondary school in the county have written to 20,000 parents warning them of what they say are the consequences of budget cuts.
In their letter the heads say that teachers will lose their jobs and class sizes will increase if the cuts are introduced by the authority's education department for the next financial year.
Powys Council confirmed that it was looking to introduce a 2% cut in all departments - meaning that more than £1m would be cut from its education budget.
Only last month councillors there voted to close two of its village primary schools in the face of rising costs.
Every parent is now being requested to write to their councillors and AMs asking them to protect the schools budget.
The letter, from the Powys Primary and Secondary Head Teacher Associations, said: "We are taking the unusual step of writing this open letter on behalf of all head teachers in Powys.
"We believe they (Powys council) are considering a budget which will result in a 2% cut in funding for education.
"This will lead to an inevitable decline in standards of achievement across all Powys schools.
"We ask you to contact your local Assembly Members and councillors and urge them to do everything possible to protect the education budget."
Head teacher of Gwernyfed High School, John Hopkins, said he could be forced to reduce staff if the 2% cut was introduced.
"Schools in Powys have suffered recurrent budget reductions over the last few years, in common with other schools in Wales," he said.
"So we were devastated to hear we were going to suffer a 2% cut across all schools - primary, secondary and special - in Powys.
"I had 38 teachers at the school, which I had to reduce to 36 in September.
"If this cut is introduced, I may have to reduce my staff by a further one or two teachers."
Mr Hopkins added that he believed pupils' education would suffer if the cuts went ahead.
"As well as fewer teachers, there will be less spending on school repairs, books and equipment.
"The Welsh assembly says that Powys Council has had a favourable financial settlement, but the council says it hasn't got enough money for the schools," he said.
The Welsh assembly says councils have had a 'good deal'
John Mason, head teacher of Archdeacon Griffiths Primary School, in Llyswen, near Brecon, added: "My school has a deficit of £18,000 and a 2% funding cut could mean £4,000 less on next year's budget.
"We would try not to lose a teacher, but other things like materials and equipment would be cut.
"This is the first time we have directly appealed to parents to get involved in this way."
A Welsh Assembly Government statement said Welsh councils had had "a good deal" in the recent budget settlement.
Councils will receive nearly £3.2bn from the Welsh Assembly Government next year.
"It is a fair deal and we are confident that it is sufficient for local authorities to meet the costs of pay and price increases and the cost of the teachers'
"It is now up to the councils to judge local needs and plan their budgets according to those needs."
Powys councillors will meet in January to decide whether to make the cuts.