School leaders are "cannon fodder", caught in the crossfire between the classroom unions and the government, according to the leader of the biggest heads' union.
Russell Hobby, general secretary of the NAHT, has accused the Department for Education of "provocation" for advising schools on how to deduct the pay of teachers taking part in work-to-rule industrial action, while issuing his strongest condemnation yet of the NUT and NASUWT teaching unions.
The DfE's intervention, "although technically correct, is unduly harsh and is as unhelpful as an escalation of the industrial action", according to the NAHT. The classroom unions have since announced plans for a programme of regional and national strikes starting in June.
But Mr Hobby also criticised the NUT and NASUWT's "damaging" campaign of industrial action, which he described as an "attempt to set the clock back in ways which are not necessary".
School leaders have found themselves "stuck in the middle" in the wake of a series of inflammatory statements from the DfE, Mr Hobby told TES. He also warned that relationships between the unions and schools could be damaged for years to come.
In December, a source close to education secretary Michael Gove was reported as saying that the department was on a "war footing", and that strikes were a price worth paying to "break the destructive power of (NASUWT general secretary Chris) Keates and (NUT general secretary Christine) Blower".
Last month, Mr Gove wrote that "the fight against the enemies of promise is a fight for our children's future... It's a battle in which you have to take sides."
The response by the biggest classroom unions was equally robust. Delegates at the NUT's annual conference this month unanimously passed a motion of no confidence in the education secretary and backed the campaign of strikes.
"School leaders feel they are cannon fodder for the different sides," Mr Hobby said. "I've probably had as tough conversations with the DfE as I've had with anyone over this, and I've been very clear that we do not want to see a provocation of the sector.
"Ultimately the people who will pay the price for that sort of conflict will be the school leaders. They have to lead these schools for years to come. If you destroy all the good relationships as a part of that then I think pupils and heads suffer."
Mr Hobby also warned that the work-to-rule action - which says teachers should not be observed for more than three hours per year, send emails outside their working hours or cover for absent staff - is adversely affecting a minority of schools.
"[Heads] don't want to break the unions: we're a union," he said. "They believe in the right to express yourself, and many of them share many of the views that are being put forward about the government. On the other hand, they've got a school to run... and once the action crosses that line from expressing frustration to damaging the education in a school, then they get equally frustrated with what the unions are doing."
Brian Lightman, general secretary of the Association of School and College Leaders, agreed that the confrontational atmosphere in the sector is "incredibly challenging for school leaders".
Ms Blower said the NUT had given Mr Gove plenty of opportunity to avert strikes. The NASUWT was unavailable for comment.
A Department for Education spokesman, meanwhile, said its advice to schools on industrial action is "in response to requests from heads who are concerned about the impact it is having".
"We agree with (the) NAHT that industrial action will disrupt pupils' education. It will also damage the reputation of the profession and place an unnecessary burden on the vast majority of hard-working teachers who did not vote for it," he said.
As well as the NUT and NASUWT's ongoing "work-to-rule" campaign, the unions are planing a strike at schools in the North West on 27 June.
This will be followed by a rolling programme of regional strike action in the autumn term, culminating in a one-day national strike before Christmas.