Militant teachers are calling for a strike to disrupt the plan for all children to return to school on March 8.
Union activist Martin Powell-Davies has said school chiefs will be 'failing in their responsibilities' of health and safety measures if they 'recklessly' open their doors.
He has urged the National Education Union, which represents 450,000 employees, to join his plans for a strike the day before children are due to return to the classroom.
Mr Powell-Davies argues that schools should be reopened in phases and that class sizes should be dropped by 50 per cent.
Militant teachers are calling for a strike to disrupt the plan for all children to return to school on March 8
He told The Sun: 'If those decisions are not met then employers will be failing in their duties. They will be creating a serious and imminent risk in not taking action to prevent it.
'They may do that, we can't fail our responsibilities.
'That's why if those rates and those steps are not met then we have to say we ballot across the employer so that if a spike does occur by Easter, we will be there with an industrial action ballot ready to protect our members and our communities.'
The activist, who is campaigning to become the NEU's deputy general secretary, is due to attend a virtual meeting with the organisation today.
The Education Solidarity Network - the campaigning faction of the NEU - will look to find a way to oppose a 'reckless full return' to schools in a week.
MPs and campaigners last night heavily criticised the union's threat of a strike because many students have spent less than two months in a classroom since the first lockdown at the end of March last year.
Union activist Martin Powell-Davies (pictured) has said school chiefs will be 'failing in their responsibilities' of health and safety measures if they 'recklessly' open their doors
SAGE, the Scientific Advisory Group for Emergencies, warned that R rate (which tracks how quickly the virus spreads) will climb back over 1 if schools fully reopen.
But chief medical officer Prof Chris Whitty said last week: 'It's universally accepted there are huge advantages for children to be in school from a health point of view, mental and physical, as well as from educational and a life-course point of view.
'We have a natural firebreak in the Easter holidays and these five weeks to work out how things are going.'
Conservative MP Bim Afolami said last night: 'Every day a school is closed is a bad day for children. Schools exist for their benefit, not the benefit of ideological teaching unions.'