Damian McNulty, national executive member of NASUWT, (National Association of Schoolmasters Union of Women Teachers), told the BBC: "Sadly we have had reports in the last 24 hours of at least six secondary schools in the North West of England where children in huge numbers are refusing to take lateral flow tests or to wear masks.
"We've got one school in Lancashire were only 67 children out of 1,300 are prepared to have a lateral flow test and wear masks.
"This is a public health emergency."
>>>Click here for more information on school Covid rules.
Mr McNulty said this was likely to be the case in other parts of the country and that there was an element of teenagers "railing against" authority, he added, made worse by some wanting to "push boundaries" with supply teachers in charge.
Lancashire County Council have been approached for comment.
On Twitter, there has been a mixed reaction to the news.
@Steelmaximus wrote: "If adults don’t have to wear masks and take tests to get into nightclubs and pubs why should kids wear masks and take tests to go to school? Good on em."
Alison Pearson wrote: "All those adults says “great one kids” let’s hope the hospital still has space for your child when they need it.
"And when the school has no teachers left, no point complaining then. Or when all the maths groups have to be taught together and your child doesn’t understand the topic. Or if your child gets long covid and is too ill to keep going to school full time."
What are the rules?
Pupils in England have been asked to take in-school Covid tests before heading back into class this week, and to wear face coverings in lessons.
However, these are recommendations and are not mandatory.
The government has stressed the guidance is temporary and will be reviewed when Plan B regulations are scheduled to expire on January 26.
Concerns have been raised on masks having a negative impact on learning in the classroom and the Government admits the evidence for using masks in schools to reduce spread of Covid is "not conclusive"