Teachers in Ontario used to get a good deal if they did not become ill: an allocation of 20 sick days a year, which could be accumulated throughout their careers and then, when they retired, cashed in for a handsome bonus.

But since the rules were overhauled earlier this year - and the bonus removed - absentee rates among teachers have shot up, prompting the need for emergency legislation in the province to allow non-teachers to cover lessons.

And if the sudden increase in sickness was not suspicious enough, the biggest spikes in absence have been on Fridays and Mondays, figures show. Under the new rules, teachers can now take up to 11 sick days a year but cannot routinely carry them over into another year.

Bruce Rodrigues, director of education for the Toronto Catholic District School Board, said teachers were “not used” to losing their sick-day allocation. Absenteeism in his schools in June was up 15 per cent compared with 2012 and the previous five years.

Mr Rodrigues said he was aware of the “speculation” that teachers were trying to use up their sick days before the end of the school year but that he did not have “solid” evidence for this.

“I don’t want to jump to the conclusion that this is the only reason,” he said. “We are giving teachers the benefit of the doubt - they are professionals and we hope they are using their sick-day allocation because there has been need.”

Scott Moreash, associate director at the Peel District School Board in Ontario, said he had heard “anecdotally” that many schools were being hit by an increase in teacher absenteeism.

“We are certainly experiencing what seems to be higher teacher absence in our classrooms,” he said. “Why is that the case? I don’t know. But we seem to be experiencing higher volume compared with last year, and higher rates on a Monday and a Friday.”

But Desiree Francis, who was president of the Ontario Secondary School Teachers’ Federation until last month, said she did not accept that there had been an increase in inappropriate absence. “What we are seeing is an awareness that comes from a shortage of cover,” she said. “I don’t think you will find teachers are going on minibreaks.”