Britain’s largest teaching union is warning that supply teachers could end up being paid only the minimum wage during school closures – because of the arrangements over how they are paid by umbrella companies.

The NEU teaching union is urging umbrella companies to use the government’s furlough scheme (Coronavirus Job Retention Scheme), where possible, through which companies can continue to pay staff 80 per cent of salary before claiming it back from the government.

However, in a letter to education secretary Gavin Williamson, the union says some of its members are reporting that umbrella companies are refusing to use the scheme because they fear they may not be able to claim all the money back.

Exclusive: Supply teachers' 'daily fight' for pay

The letter, signed by joint-general secretaries Kevin Courtney and Mary Bousted, highlights the three elements that often make up a supply teacher’s pay packet from an umbrella company, which are pay (the minimum wage), bonus and commission.

Coronavirus school closures: 'Uncertainty' over supply teacher pay

"The pay element will be expressed as equal to the minimum wage, but the reality is that the combined value of these three items is the actual regular earnings of the worker," it says.

"Unfortunately, the remaining elements of the worker’s earnings are not only described as commission and bonus elements but are also often expressed as discretionary in the contract – even though they are treated as obligatory payments and are not performance-related."

It says that umbrella companies fear they may only be able to claim back the "pay" element in the furlough scheme – following HMRC guidance which states that bonus and commission can’t be included when calculating the 80 per cent of pay that furloughed workers get.

The letter states: "We wish to seek a confirmation from the government that where umbrella companies do claim 80 per cent of workers’ pay based on full pay (including the element of pay expressed as bonus or commission, whether discretionary or otherwise) they will successfully recover that amount, and that HMRC will not subsequently seek to claw back the bonus and commission elements from the company."

It adds that, at present, “the arrangements for paying workers engaged via umbrella companies are constructed in such a way as to suggest that our members are contractually entitled only to the national minimum wage.

"We are concerned that swathes of our teacher and support staff members will be left out of pocket."

The NEU action follows weeks of uncertainly for many of the 13,000 supply teachers in England. Many are facing a daily battle to get paid, and say new government guidance has made it unclear as to who is responsible for paying them.

The letter also says that few headteachers are familiar with the term “contingent worker”, as used in DfE guidance, and that few heads will be aware that it refers to supply teachers and supply teaching assistants.

It states: “Many [school leaders] will not, therefore, recognise that the guidance applies to staff who have been working in their schools on non-permanent contracts, such as supply workers or music teachers. Many such staff have had their contracts terminated inappropriately and without consideration of the contingent worker guidance”.

The DfE said the education secretary would respond to the NEU letter “in due course”.

A spokesperson said: “We know this is an extremely challenging time for everyone, and many people are concerned about their job security.

“The government is doing everything it can to support people in work, including supply teachers. Our published guidance includes information about how schools and agencies can support supply teachers.”