The warning was issued in a letter by the Strategic Head of Ysgol Dyffryn Nantlle – which has around 450 pupils aged 11-18 – in Penygroes, Gwynedd – as part of an approach recommended by the local council.
In the letter, the school was told not to give children food “if their debt has not been cleared, or, in the future, to children whose accounts do not have enough money to pay for lunch”.
A deadline of November 19 has been set for parents to get their children’s accounts up to date.
The letter, which has sparked fury among parents, the letter was issued as the Welsh school reportedly ran up a debt totalling more than £1,800 last year.
It was accumulated by some 70 families, with nine parents owing more than £50 and three of them owing more than £100.
Since the letter was shared online, it has received backlash from a number of parents across the UK.
“Absolutely shocking, one parent wrote. “What the hell’s wrong with system, the child might not know mam and dad are struggling to pay, it might be the only food that child eats that day.”
Mr Foden has apologised for the approach but said the “scale of the default means that something clearly has to be done”.
The Gwynedd Council are urging parents who are having financial issues to contact the school as some may be entitled to free school meals.
Welsh Conservative Shadow Minister for Education, Laura Anne Jones MS, said: “Gwynedd Council should immediately reverse this decision and work with parents to find a solution that keeps children fed whilst ensuring monies are collected.”