The March Budget, which set out the Government’s spending plans, has cut the funding dedicated to repairing school buildings by £100m.
The Department for Education's (DfE) capital budget next year is £4.5bn, compared with £4.6bn this year.
Trade unions in the Joint Union Asbestos Committee (JUAC), which campaigns to reduce asbestos in schools, described the move as “irresponsible”.
John McClean, chair of JUAC, said: “Any real-terms decrease in capital funding for schools in this Budget will raise the risk from asbestos for children and staff.
“School budgets are already at breaking point after more than a decade’s funding freeze, and many school buildings are literally crumbling as repairs become unaffordable.”
Around four-fifths of school buildings in England contain asbestos, according to the Department for Health's own estimate.
Recent research by the NEU teaching union has revealed that 3,731 schools need immediate repair and a further 9,872 need work within two years at the latest.
The union's joint general secretary Mary Bousted said: “Spending on school buildings has fallen dramatically since 2010; it is now 42 per cent lower than under the last government. We greatly regret the government’s neglect.”