Strike action over funding cuts in England's schools has been backed by the National Union of Teachers.
The union's annual conference voted to use an existing ballot over funding to stage a one-day school strike in their challenge over budget shortages.
Teachers say that spending cuts are leading to job losses, timetable cuts and courses being cancelled.
But the Department for Education says that spending on schools is at the "highest level on record".
But this claim has been rejected by teachers, who point to a real-terms 8% cut as a result of unfunded extra costs, as well as changes from a new funding formula.
Jo Yurky, founder of the parents' campaign group, Fair Funding For All Schools, claimed that budget shortages had left schools worrying about money for heating - to the extent that in one school pupils had to wear their coats and hats in the classroom.
'I've had enough'
Speaking after the vote at the union's conference in Cardiff, the NUT's general secretary, Kevin Courtney, said he would consult his union's members before pushing ahead with any strike, national or regional.
However, as the union has an active ballot for strike action valid until August 31, this could be used as the legal basis for strikes.
He said: "There are places where the cuts are so bad and the degree of concern so big that strike action is a real possibility. We will consult with colleagues in the regions about the readiness of members to do this.
"If Justine Greening announces the funding formula is changing to make things even worse in some areas, that would be very likely to raise the level of anger in those areas to a point where action will take place."
The NASUWT teachers' union, holding its annual conference this weekend in Manchester, has warned that schools are relying on parental donations for funding - and BBC News website readers have sent in their own experiences of being asked for extra money by schools.
Speaking in favour of a one-day strike at the NUT conference, Cleo Lewis, a delegate from Lewisham, south-east London, said: "I've had enough. It's just too much. Nothing gets changed by sitting around and discussing.
"We can sit and discuss until we are blue in the face.
"The government are not accepting our nice words. We need to show them we are serious."
James Kerr, also from Lewisham, south-east London, said: "We need a strategy that can win on cuts."
Jacqueline Baker told the conference that in her school a teacher had been asked to teach Spanish without knowing a single word of the language.
But a Department for Education spokeswoman said: "We have protected the core schools budget in real terms since 2010, with school funding at its highest level on record at more than £40bn in 2016-17 - and that is set to rise, as pupil numbers rise over the next two years, to £42bn by 2019-20.
"We recognise that schools are facing cost pressures, and we will continue to provide support to help them use their funding in the most cost effective ways, so that every pound of the investment we make in education has the greatest impact."