Schools should avoid unnecessary expenditure before April as the threat to spending surpluses in Northern Ireland has not been resolved, the Department of Education has warned.
Education Minister Caitriona Ruane's officials have written to principals and boards of governors urging belt-tightening as she lobbies for more money.
There is continuing uncertainty in schools across Northern Ireland because the Treasury has removed millions of pounds of underspend which some head teachers roll over to fill posts like classroom assistants the following year.
The Democratic Unionist Party (DUP) warned that axing the end-year funding will cause redundancies this year. But Ms Ruane intends to shift £41 million from the building budget to pay instead for services and staffing.
Her department's letter said: "I would urge schools not to abandon their practice of sound financial management and to avoid any unnecessary expenditure before the end of the current financial year.
"While work continues to agree a way forward, this is more important than ever given the resource constraints and difficult budget settlement."
In the past schools were able to carry any unspent sums into the next financial year. However the Treasury intends to claw back a Department of Education reserve of £87 million, £56 million of which is used by schools.
The Education Minister has raised the issue of surpluses with Finance Minister Sammy Wilson and other members of the Executive.
The department's letter said: "The minister is not prepared to let the matter rest and will do all that she can to maintain the entitlement of schools to their surpluses."
Money for computer technology and professional support will also be cut, with education and library board costs reduced. Ms Ruane said she was doing all she could to prevent redundancies and there was no point in having lots of new classrooms with not enough staff in them.