Scotland's largest teaching union has warned SNP ministers they face strike action in schools as it demanded that children only attend class part time.
Larry Flanagan, the EIS general secretary, said he knew of three schools in Glasgow with "hundreds and hundreds" of pupils and more than a third of staff absent.
He accused the Scottish Government of being more concerned with their "political agenda" than staff safety and urged them to "face up" to the spread of Covid in schools.
Among his demands were the reintroduction of so-called 'blended learning' - children only being in class part-time - and two-metre social distancing. The latter would make it impossible for all pupils to attend simultaneously.
Mr Flanagan confirmed that his members were being asked whether they would be "prepared to consider industrial action in terms of a safety strike protest".
It is understood this would involve balloting for strike action in individual schools or local authorities where there are higher rates of infection, and where teachers believe safety measures are insufficient.
However, Gregor Smith, the interim chief medical officer, insisted there was "no compelling evidence of significant transmission" of Covid between young pupils, and transmission in older pupils was generally lower than in adults.
- EIS (@EISUnion) November 13, 2020
The latest official statistics show that Covid-related pupil absence levels hit 4.2 per cent on Nov 10, but only 758 of the 29,486 absent pupils had Covid-related sickness.
Absence levels were higher in secondary schools (5.3 per cent) compared to primary schools (per cent).
However, the Liberal Democrats said yesterday that Scotland has undertaken 20 per cent less Covid testing per capita than England.
Citing the Glasgow schools with lots of children off, Mr Flanagan said: "That is not a good educational experience. If we want to keep schools open, let's move to blended learning. Let's introduce two-metre physical distancing and let's ensure that schools are safe places."
He added: "I think the Scottish Government should face up to that and stop being so concerned about its political agenda and start thinking about the health and safety of staff who are working in schools."
But parents' group Us For Them Scotland backed Nicola Sturgeon's decision to keep schools open, even in those areas entering the highest Level 4 restrictions later this week. This will see non-essential businesses and shops close.
Jo Bisset, the group's organiser, said: "We know there are influential groups who've wanted schools shut right from the start, and now strike action is being used as another tactic to force this through.
"All of this serves to damage the wellbeing and prospects of children. Schools are and should be considered critical infrastructure."
She added: "Blended learning was, at best, a farce. For many in the poorest areas, it cast children adrift from an education system which they're now unlikely to catch up with."
Responding to the FM's comments - Larry Flanagan of the @EISUnion says if we want to keep schools open - we need to move to blended learning
He adds the Scot Govt needs to stop being so concerned about its "political agenda" and be more concerned about the safety of staff pic.twitter.com/Wq0KLAMK4F
- Alan Smith (@Political_AlanS) November 16, 2020
Speaking at her daily briefing, Ms Sturgeon said it was her "objective and intention" to keep schools open in Level 4 areas
Dr Smith said ONS data suggested teachers were no more likely to be infected than people of a similar age in other professions.
Meanwhile, the Scottish Lib Dems said Scotland had conducted 445 Covid tests per 1,000 people compared to the English figure of 539.
Willie Rennie, the party's leader, said that if the SNP had "insisted on negative tests for people discharged from hospitals to care homes, the worst scenes of this pandemic could have been avoided."
A Scottish Government spokesman said: "Testing capacity used by Scotland through the UK Government testing route fluctuates in response to the demand and will vary between different countries in the UK."