A curriculum restructure at seven secondary schools in Yorkshire and the Humber will lead to more than 88 jobs cuts as creative subjects are ditched in favour of a more academic focus, the National Union of Teachers has warned.

The union will ballot staff at seven schools – De Warenne Academy, Ash Hill Academy and Don Valley Academy in Doncaster; Melior Community Academy in Scunthorpe; the South Leeds Academy, John Whitgift Academy in Grimsby; and Manor Croft Academy in Dewsbury – over potential strike action following an announcement by the School Partnership Trust Academies.

Schools Week understands the trust is seeking to make voluntary redundancies in 85 posts – 48 teaching posts and 37 support staff – and a further three compulsory redundancies as it is reducing the number of GCSEs some pupils study.

It is believed that pupils wanting to study subjects such as music will have to opt in to after-school classes under the new system, which has come about after the trust expressed fears children were studying too many subjects and schools were “overstaffed”.

The shake-up, first revealed by the Yorkshire Post this morning, will require schools to prioritise academic subjects so the schools can perform better against the government’s new “progress 8” performance measure.

The measure rates schools based on pupils’ performance in the five EBacc subjects – English, maths, science, history or geography and languages – plus their three highest non-EBacc grades.

Subjects like music can be included in progress 8, but are less likely to be prioritised by schools which focus more on routes for pupils with subjects that can count across any of the 8 slots, such as triple science or an extra humanities subject.

Emma Forrest, an NUT organiser involved in negotiations with the schools, said the trust’s response to disappointing results had been to “focus completely on progress 8 to the detriment of other subjects”.

“It’s hard to pin SPTA down in terms of the reasons for the re-structure,” she said. “They have always told us that this is about finances, and now suddenly it’s not about finances. They have not mentioned over-staffing to us once.”

It is not the first big hurdle faced by the trust in recent years. Last December, it was revealed that SPTA would be stripped of 3 of its schools in Nottinghamshire following fears they were isolated from the rest of the organisation, and similar fears were expressed about Don Valley, Ash Hill and de Warenne, which are all rated inadequate by Ofsted.

In March, the trust was namechecked by Ofsted chief inspector Sir Michael Wilshaw when he launched a scathing attack on the academy trust model, warning that some had “manifested the same weaknesses” as the worst-performing local authorities and “offered the same excuses”.

A spokesperson, who confirmed the trust had only been notified of a ballot at four of the seven schools, said the trust had an in-year deficit of £3.2 million last year and was projecting a further in-year deficit of £6.8 million this year.

The trust said it had identified three potential compulsory redundancies following work to “ensure that staffing structures reflect the academy and student needs”.

“We believe that students need a good grade in both English and Maths to be successful in accessing the next level of education, training or employment,” he said. “These will be the priorities for our schools moving forward, alongside a broad and balanced curriculum.

“We recognise that the trade unions are trying to protect their members’ jobs in a very difficult time and we will continue to work with them supportively. However, the trust must take positive action to support and improve student outcomes and deliver value for money to parents and the wider community.”

The structural changes are similar to those employed by Outwood Grange Academies Trust, which is working in partnership with SPTA. The trust was keen to play down rumours of a take-over after it was revealed Outwood’s second-in-charge had taken over the helm at SPTA.