A network of school leaders in Worcestershire has expressed “grave concerns” about an “immediate funding crisis” caused by staff pay rises.
In a letter to MPs, the Worcestershire Association of Secondary Head Teachers said the 5% increase was “significantly higher” than budgeted for.
Schools faced a choice between cuts to staff or maintenance, the letter said.
The Department for Education said core funding had increased by £4bn this year.
The letter, written on behalf of 32 school leaders in the county, was signed by Bryn Thomas from Wolverley CE Secondary School.
Mr Thomas said although the pay award helped mitigate cost of living increases, it was not “fully-funded” and meant schools faced “an immediate budgetary pressure”.
“The typical secondary school in Worcestershire is facing a £150-£200K increase in staffing costs this financial year,” he wrote.
In a survey of association members, all 22 respondents said staff cuts were “likely” in their schools and could result in larger class sizes and a narrower curriculum.
Nearly half the schools told the association they were also likely to reduce spending on maintenance.
“What little is left is being squeezed by inflationary pressure which is not matched by school budget increases,” the letter added.
Mr Thomas told the BBC without additional funding the school would be forced to operate at a loss after its fixed deal on energy ended in April.
“If we’re not protected we’re looking at a trebling of that £125,000 bill,which will mean another £250,000 will come out of the £900,000 that we have to run our school,” he said.
“So really this isn’t sustainable. If these pay rises aren’t funded and we have to go into a deficit then paying it back will mean long-term we spend less money on the students and in the school.”
The letter was sent to Worcestershire MPs Rachel Maclean, Mark Garnier, Harriet Baldwin, Robin Walker, Sajid Javid and Nigel Huddleston.
Mr Garnier, Conservative member for Wyre Forest, told the BBC he had spoken informally to most of his Worcestershire colleagues, who were supportive of the school’s plea for additional funding.
“We’ll be getting out there and trying to see if we can persuade the government to follow up with the commensurate funding,” he said.
Ms Maclean’s office told the BBC she would pass the correspondence to the Education Secretary Kit Malthouse.
A Department for Education spokesperson said schools were being supported with £53.8bn in core funding.
“All schools will benefit from the Energy Relief Scheme, capping how much schools need to spend on their energy and giving them greater certainty over their budgets over the winter months,” they added.