Leading independent schools warned they would have to close their cadet forces as a result of a government cut in their funding.
The Ministry of Defence has told schools they will have to pay £150 per per cadet to allow them to extend cadet training facilities to a further 100 schools. The levy will be phased in over the next four years.
Leaders of the Headmasters' and Headmistresses' Conference - which represents 250 of the country's elite private schools including Eton and Harrow - warned the move could decimate existing cadet forces and bring to an end more than a century of military traditions in private schools.
At present, there are 260 CCF units operating in schools - the majority (200 of them ) in independent schools.
The threat comes after Prime Minister David Cameron spoke of his plans to expand CCF units in schools, saying: "I want many more more people to gain this kind of experience no matter what their background is."
However, as a result of expanding the subsidy for weapons training and exercises - in training camps from the 260 existing schools - the MoD has said it will have to introduce the levy and stop payments for volunteers who run the units.
Thomas Garnier, head of Pangbourne College in Reading, said the levy would cost his school £27,000 a year. "I just can't afford it," he added. "We're a small school but we live on the margin. I can't accept the increase in the budget for the CCF.
"We will have to look afresh at the vallue the CCF offers. We can't put the charge on to the parents."
He said that at the very least he would have to make the CCF voluntary, "thus cutting by half the number of students involved in it".
He added that many schools might have to axe their provision entirely with the prospect for the Armed Forces that recruitment in future "is clearly going to suffer".
Richard Harman, chairman of the HMC and headmaster of Uppingham School in Rutland, added: "If this goes ahead, many CCFs will shut down. we would either have to charge parents significant amounts of more money to do it or find significant funding from elsewhere in our budgets.
"In actual fact, we're all looking a bit more closely at how much running a CCF costs us at the moment."
In a letter to heads, Major General John Crackett, assistant chief of the defence staff (reserves and cadets), said: "I recognise that this will come as unwelcome news to some. Even so, I firmly believe that this approach will deliver a more equitable and sustainable funding model for CCFs."
Under the proposals, the MoD will stop funding for volunteers to run the service from September 2016 and phase in the £150 levy from September 2017.
The heads are asking for Major General Hackett's letter to be withdrawn and for a new consultation on the proposals to belaunched.