Supply teachers across Scotland are refusing en masse to provide cover for winter illness in a bid to increase the pressure on ministers to reinstate higher pay rates.
Next Monday, they are launching the so-called "Low Pay Flu" stand, aimed at hitting schools at a time when absences through sickness will be highest.
The Scottish Supply Teachers network said growing numbers of supply staff would turn down requests to step in for staff during the flu season in protest at controversial low pay rates for short-term cover introduced last year.
A statement from the campaign group, set up by Glasgow maths supply teacher Sumera Tarbard, warned: "Supply staff are professional people, able and willing to do a vital professional job, so it is only right and proper that they are paid professional pay.
"Michael Russell (education secretary) has said all along that last year's agreement was not ideal and he has been proven correct. It's now time for Cosla and the Scottish government to reintroduce the correct rates."
John Stodter, general secretary of the Association of Directors of Education in Scotland, said the impact of the threatened boycott would depend on which supply teachers withdrew their labour.
He warned: "There's some illness going around, with the winter vomiting virus in some parts of the country, and February is traditionally a month when we need all the resources we can get."
At the start of this year, the Scottish Government told TESS that further action was likely "in the new year" by way of response to growing anger over supply pay rates (6 January).
However, a government spokesman merely repeated this week that the deal was the "best possible" and the situation was being "closely monitored".