School principals from Co Down have written to the secretary of state warning what budget cuts will mean for them.
In a letter seen by UTV, they say the only way they can reduce costs to bring them in line with the budget he has imposed is by cutting the number of school staff.
They say school funding has been insufficient in the last 10 years - but that these new cuts will be catastrophic.
One of the principals, Kevin Donaghy from St Ronan's in Newry, says he's extremely worried.
He said: "Our allocation would be over £1m to run our school, out of that 96% is going on paying for staff costs.
"That has gone up from 91% and that is because of a reduced allocation to our school, but also the fact that staffing costs have increased.
"I am left with £57,000 to run my school to pay for everything."
In reply, Chris Heaton-Harris once again said the best way to address funding issues is for politicians to get back into Government at Stormont.
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