The government must fund schools sufficiently, tell academies to observe national terms and conditions and promise “meaningful talks” to avoid strike action by teachers next week, the National Union of Teachers has said.

In a letter to the education secretary Nicky Morgan, the union’s acting general secretary Kevin Courtney has expressed regret that next Tuesday’s strike is now a week away with no resolution on the horizon – and made a final appeal for three concessions to stop the walk-out.

The union is striking to demand increased funding for schools, guaranteed terms and conditions for staff in all institutions, including academies, and resumed negotiations on teacher contracts to address problems with workload.

But the union has been criticised for proceeding with a strike after a ballot which less than a quarter of its 210,000 members voted in, despite the fact that 91.7 per cent of those who did vote backed strike action.

Courtney, who is leading the union on an interim basis as he campaigns to become its official leader following the recent departure of Christine Blower, said the government should fund schools sufficiently “to cover the increased staff costs you have imposed on them”.

He said the government should also tell academies they must “at least have regard to the national terms and conditions” and called on ministers to pledge “meaningful talks to look for a full resolution of the dispute”.

“No teacher finds taking strike action easy but the situation in our schools needs to be urgently addressed,” said Courtney. “School budgets are being cut to the bone. The effect on children’s education is clear.

“Teachers’ terms and conditions are being deregulated and worsened through the academy programme. Headteachers are spending time on school negotiations which should be spent on education. This is unnecessary, time wasting and ineffective.”

Courtney said last week’s EU referendum had “thrown the country into a period of uncertainty” and said unions wanted to see education debated and “at the forefront of candidates’ campaigns” in the upcoming Conservative leadership race.

“Now more than ever in these uncertain times we need a properly funded and staffed education system,” he added. “I have written to Nicky Morgan asking her to take actions that would protect our children’s education. Our country’s pupils and teachers deserve a positive response.”

The Department for Education has urged the union “not to proceed” with the strike and “resolve pay disputes at the negotiating table rather than playing politics with children’s futures”.

A spokesperson said: “It is disappointing the National Union of Teachers has chosen to take unnecessary and damaging strike action, which less than a quarter of its members voted for.

“It is even more disappointing when we have offered and committed to formal talks between ministers and the unions to address their concerns about pay.”