Head teachers’ letters warning of the “dreadful state” of school funding are being sent to parents in at least 3,000 schools across 17 counties on Friday.
The mass mailing urges parents to raise the “current financial difficulties” in schools with all prospective candidates “on the doorstep”.
It comes in the week the three main parties pledged more money for schools.
Schools in England are being required to find savings worth £3bn to deal with rising cost pressures.
The letter, being sent home to parents with pupils, says: “I am writing to you in order to raise the issue of school funding and the significant current financial difficulties that all of our schools are now facing.
“During all of our campaigning work to improve funding for each and every child in each and every school, we have been careful not to become involved in a politically biased or partisan way.
“Head teacher colleagues and I feel that ahead of the forthcoming general election it is crucial that parents, carers and all other interested parties raise the issue of school funding ‘on the doorstep’ with all prospective candidates.
“It would be naïve to think that school funding is the only issue affecting everyone’s lives but school finances are in such a dreadful state that we believe that it is vital to urge you to raise it as a key issue prior to 8 June.
“As professionals we are only interested in securing fair and adequate funding for the children that we educate. This is under severe threat and has influenced our decision to contact you in a collaborative manner.”
On Thursday, the Conservatives pledged an extra £1bn a year for schools – on top of its current spending plans and partly funded by axing the right for infant pupils to have school meals for free.
On Tuesday, Labour pledged to invest more than £20bn in schools in England by 2022, as part of a package of education pledges.
And on Wednesday, the Lib Dems proposed spending £7bn over the same period to protect per pupil spending.
Jules White, head teachers of Tanbridge House School near Horsham, West Sussex, said he and his fellow heads were pleased that all the political parties were beginning to recognise that schools are vastly underfunded, but said that they needed to see the detail of the spending proposals.
Head teachers’ unions have been warning how schools are having to make tough decisions as their budgets are being forced to stretch further.
Some are planning to make staff redundant or cut courses, while others have sought to reduce running costs by switching off lights or heating.