TORONTO -- A looming provincewide teachers' strike and vocal opposition to a new sex-ed curriculum have thrown Ontario's education system into turmoil.

Elementary school teachers are taking strike action starting Monday, likely in the form of a work-to-rule campaign -- a move the province's education minister says is motivated by the union's "general desire to have a strike" rather than any one issue.

The planned job action comes as more than 70,000 high school students in the province sit home because teachers at three boards are on strike.

At the same time, thousands of parents are voluntarily keeping their kids home to protest Ontario's updated sex-ed curriculum, which will be taught starting in September.

Opponents say the new program is not appropriate for school-age children and does not align with their values. Many of the parents complain about mentions of same-sex relationships, gender identity and masturbation.

In Toronto, about 34,000 elementary students were absent Monday, the first day of a planned week-long campaign largely organized through Facebook. That's more than double the absences recorded last Monday. The number of absences dropped to about 28,000 on Tuesday.

At least one of the city's elementary schools had an absentee rate of more than 90 per cent. Supporters of the curriculum say the opposition is largely founded on misinformation.

Wynne said Tuesday that it's concerning those children will not be learning valuable math, science and language lessons this week. The curriculum, which hadn't been updated since 1998, brings Ontario in line with other jurisdictions and gives kids "the information they need to keep themselves safe," she said.

The labour unrest marks the end of more than a decade of relative peace with the teachers. After a succession of labour disruptions during Progressive Conservative governments, these are the first full strikes to hit Ontario schools since the Liberals took power in 2003.

Premier Kathleen Wynne said she knew this would be a tough round of bargaining because the government, which is facing a $10.9-billion deficit, has said there is no new money for wages.

"That's a hard pill for public-sector employees to swallow. I get that," she said.

Both the elementary teachers' union and their secondary schools counterpart say their bargaining disputes with the government are not about money, citing factors such as teacher working conditions, class sizes and teacher preparation time.

The Elementary Teachers' Federation of Ontario told members they will be on a work-to-rule campaign starting Monday, which means they'll refuse to administer standardized tests, prepare report cards and participate in professional development sessions.

The union memo has been mentioned in media reports and Ontario's education minister said Tuesday she had seen it, but the head of the union won't say until Friday what form their job action next week will take, be it work-to-rule or a full strike.

Education Minister Liz Sandals said Tuesday she has heard from government negotiators at the contract talks that the labour unrest isn't about one issue in particular.

"It just seems to be a general desire to have a strike," she said. "The conditions to not have a strike were pretty unrealistic. I'm not going to get into the individual issues."

When asked if she was considering back-to-work legislation, Premier Kathleen Wynne said the Education Relations Commission determines when a strike or lockout places a school year in jeopardy for students, and that has not happened yet.

These negotiations are also the first since the province brought in a new bargaining system with both local and provincial talks. Wynne said it seems that it's difficult for the local tables to settle before there's a central deal.

Central talks between the Ontario Secondary School Teachers' Federation and the province and school boards have also broken down.