More than 1,000 councillors in England have written to the education secretary urging the government to give schools billions of pounds in extra funding.
The letter to Damian Hinds calls for an end to spending cuts and for adequate funding for special needs (Send).
A report last year by the Institute for Fiscal Studies said total spending per pupil in England had fallen by 8% in real terms between 2009-10 and 2017-18.
The Department for Education says Mr Hinds is making the case for schools.
The signing of the letter has been organised by the National Education Union’s councillor network, which is supported by the fairer funding campaign group, f40.
The letter, which is to be handed in to the Department for Education (DfE) headquarters in Westminster later, says: “Our excellent state-funded schools have lost out in billions of pounds in funding since 2015.
“The funding crisis has become so overwhelming that according to the Education Policy Institute, almost a third of all council-run secondary schools are now in deficit, and eight in 10 academies are in deficit according to last year’s Kreston UK report.
“Many schools are now desperately overwhelmed as more and more students are competing for fewer and fewer resources.
“Compounded by biting cuts to local council services, in addition to the teacher recruitment and retention crisis, the current settlement is not tenable.”
Chairman of the f40 group and Conservative councillor in West Devon, James McInnes, said: “The f40 campaign for fair funding has given its full support to the NEU’s letter to Damian Hinds and is pleased it’s been so well supported by councillors from across the country.
“It’s clear that elected representatives are unhappy with the government’s handling of school funding and are demanding an increase in budgets, as well as adjustments to the way funding is allocated.”
Head teachers across England have also protested about their budgets, saying they have been forced to ask parents for extra cash for basic supplies.
How has the government responded?
A spokesman for the DfE said: “School funding in England is at its highest ever level and since 2017, the government has given every local authority in England more money for every pupil in every school, while allocating the biggest increases to the schools that have been most underfunded.
“In the last year, we have also announced an extra £400m of capital funding for schools from the Treasury.
“Nonetheless, we do recognise the budgeting challenges schools face. That is why the education secretary has been making a strong case for education spending across government ahead of the next spending review.
“We are also aware of the funding pressures faced by local authorities on high needs – that’s why we recently provided the £350m in revenue and capital funding, on top of increases we had already promised.”