Tadcaster Grammar School in York wants parent contributions
Parents at a North Yorkshire state school are being asked for monthly payments towards its running costs.
Tadcaster Grammar School has asked for "voluntary" contributions in response to "very significant rises in costs" - including teachers' pensions.
A letter from head teacher Martyn Sibley said the school needed to find an extra £1,100 per year per teacher.
One parent said it felt like an "imposition" to be asked to pay. The school is yet to comment.
State schools in England are allowed to ask for payments, but they must make clear there is no obligation to contribute.
The school, which is rated as "good" by Ofsted, has been consulting with parents on the amounts.
'A dismal impact'
Chris McGovern, of the Campaign for Real Education, said: "It's not about money, it's about quality of teaching.
"The fact is, parents have to work within their own budgets and the school, I think, is making a mistake if it thinks the more money you spend, the better education you get."
The National Union of Teachers (NUT) said three out of four head teachers were worried about funding.
Richard Raftery, from the NUT, said: "I can fully understand why schools start doing desperate things.
"We've had anecdotal evidence of some schools saying to their staff - if you're ill and you're ringing in the morning, just see if you can drag yourself in later in the day because our supply budget is exhausted."
Mr Raftery added: "Across the whole range of things there will be a dismal impact and ultimately it comes back to the government not facing up to its responsibilities."
The Department for Education said it was taking "difficult decisions" necessary to ensure the national schools budget was protected.
North Yorkshire County Council said it was pushing for a fairer distribution of funding to schools.