Reports of teachers being denied time off to receive their Covid-19 vaccine are 'widespread', it was claimed.
Dr Patrick Roach, general secretary of the NASUWT union, said some employers are refusing to listen to teachers' concerns over safety.
He called on politicians to “step in” to help deal with the issue.
Addressing the NASUWT’s annual conference on Sunday, Dr Roach highlighted what he called shoddy practices.
“Ministers mustn’t only listen to the concerns of the profession – they need to act on them. Listen to teachers’ concerns about those employers who have felt emboldened to pursue ‘business as usual’," he said.
“Listen to teachers’ concerns about uncaring employers who seek to discipline teachers if they contract Covid, or tell teachers they can’t have time off to receive their Covid vaccine jab.”
Dr Roach said reports of school staff being denied time off to get their vaccination were widespread.
“I wish it was only a one-off but the number of times that’s come across my desk I cannot begin to tell you. It has been pretty widespread.
He said the education secretary issued further guidance to schools on the matter after concerns were raised by the the teachers' union.
He warned that such practices could play into issues around “vaccine hesitancy” and “slow down the system for everyone else”.
In his speech to the conference, Dr Roach launched an attack on the government over its handling of the pandemic and its actions towards teachers.
He said staff “must not be coerced into working yet longer hours or delivering summer schools” to deliver short-term fixes.
“Teachers’ commitment and resilience have already been tested to the limit. They don’t need more exhortation and empty words – they need action by government which puts teachers first,” he said.
His comments came after the Education Secretary Gavin Williamson said that a change to the summer holidays and longer school days were being considered as part of long-term recovery plans for pupils who have missed out on lessons.
“Government needs to stop looking for quick fixes and grabbing media headlines. Instead of catch-up, they need to catch on – catch on to the long-term damage inflicted by their own policies," Dr Roach told the conference.
“Catch on to the need for much greater investment in all those services that will provide the foundation for the education recovery that children and young people need.
“If we are to aspire to have the best country for children to grow up in, we will need more than catch-up and recovery. We need a plan for education renewal. And we want a recovery, a renewal – that’s teacher-led too.”
On Sunday, Labour leader Sir Keir Starmer told the conference there could be "no return to business as usual".
“The challenges of the pandemic have thrown into sharp relief the inequalities that were already embedded in our society."
In a video message to delegates, Mr Starmer said he knew “first-hand” that teachers had risen to the challenge, as his children were in school throughout the year due to his wife being an NHS worker.
“Their teachers’ and all the school staff’s commitment and dedication has been nothing short of extraordinary. And I know that is the case in schools right across the country,” he said.
A Government spokesperson said: “We are very grateful to all the teachers and staff who have worked so hard throughout this pandemic, and we welcome the support of schools and colleges in encouraging vaccine take up and enabling staff who are eligible to attend booked vaccine appointments.
“The latest advice from the joint committee on vaccination and immunisation is to continue to prioritise people by age, and teachers and staff who are over 50 are receiving vaccines within the first roll-out.”