It is "disappointing" that the government will not make free school meals vouchers available over the Easter holidays, teachers have said.
Heads have said the national voucher scheme, officially launched today by the Department for Education (DfE), will be "welcome news" for schools.
But concerns have been raised that low-income families will struggle to cope over Easter, as the support will not be extended over the two-week break.
Coronavirus: Free school meals vouchers available today
Background: Vouchers for FSM pupils backed by DfE
Kevin Courtney, joint general secretary of the NEU teaching union, said: "It is disappointing that the government has chosen not to make sure that free school meals vouchers are available over the Easter fortnight.
"This isn’t a normal school holiday and we are asking teachers and support staff to volunteer to work, in support of the NHS.
"Families on low incomes will need access to school meals during this fortnight, particularly as food banks are seriously overstretched and it is much harder to shop affordably at the moment."
Sam Freedman, CEO of the Education Partnerships Group consultancy, said on Twitter: "Government expecting schools to be open over Easter but isn't funding free school meals over the holidays. Not really ok @educationgovuk."
And youth worker Daniel Brown said: "Food vouchers for 1.3 million children to replace free school meals are welcome – will it be available outside of term time; i.e. Easter?
Mr Courtney added: "Recent government statistics showed that 4.2 million children are trapped in poverty – this is likely to rise when the current public health crisis subsides.
"Food vouchers might be the only realistic and manageable intervention for many schools at the moment, but we mustn’t normalise the idea of food provision to poorer families.
"We must banish food poverty once the health crisis is over, through better wages and secure employment."
Schools will today receive an email from the DfE's chosen provider, Edenred, enabling them to obtain weekly vouchers worth £15 for vulnerable pupils.
Until now, many schools have been making their own arrangements for the collection or delivery of free meals.
They can continue to do so, but where this is not possible, today's development will allow them to provide vouchers to families electronically, or as a gift card for those without internet access.
Government guidance updated today states: "It is for schools to decide locally how their arrangements for free school meals will operate.
"While the vouchers are for term time only, if there is a local arrangement to supply food that the school and the supplier intend to continue over this period then that can be agreed and managed locally.
"This would need to be manageable within schools’ existing resources, as there will not be additional funding available for this purpose."
The DfE has been approached for comment.