Ontario's public high school teachers have filed for provincial conciliation, a move that sets the stage for a province-wide strike in September.

The Ontario Secondary School Teachers' Federation (OSSTF), the union representing the province's public high school teachers, confirmed the move to CBC News on Friday afternoon.

In late May, provincial lawmakers sent striking high school teachers in the Peel, Durham and Rainbow school districts back to the classroom, passing back-to-work legislation by a vote of 64 to 18. The Progressive Conservatives supported the governing Liberals' bill, which was opposed by the NDP.

Elementary teachers ramp up work-to-rule

Before the OSSTF made its announcement Friday, the province's elementary teachers ramped up their own work-to-rule campaign by withholding comments on end-of-year report cards. Public elementary school students can expect grades but little input on how they got them.

The move is the latest step in the work-to-rule campaign by the Elementary Teachers' Federation of Ontario (ETFO), which represents 76,000 educators in public elementary schools across the province.

'There's a lot of information that should be in report cards other than just dropping the grades on the table and running.' - Education Minister Liz Sandals

Teachers are also planning to leave it to their school board to input the marks. Extra staff may have to be brought in to handle the extra work, board officials say.

Most Toronto public elementary school students had the day off Friday due to a professional activity day for their teachers.

Parents outside Clinton Street Public School said the situation is not ideal, but they don't mind not seeing comments on their child's report card.

"At this point in the school year you probably know what to expect in terms of the comments, to be quite honest," one mother told CBC News.

"I mean, you have been communicating with the teachers throughout the year. Report cards just give you a snapshot of what you probably already know."

"Of course I would like to hear everything that my teacher has to say about my son," one father said. "But I do support the teachers a hundred per cent."

Education minister concerned

Last month, Education Minister Liz Sandals said she was concerned about the work-to-rule campaign's potential impact on report cards.

"There's a lot of information that should be in report cards other than just dropping the grades on the table and running," Sandals said. 

On Friday, opposition leaders at Queen's Park accused the Liberal government of dropping the ball on negotiations with teachers.

"When you hear the education minister say they're mystified and confused why there's even a strike and they seem to rely on this two-tier track of negotiations that hasn't worked, that isn't working, it's certainly going to lead to future labour disruptions," Progressive Conservative Leader Patrick Brown said.

"So we're flagging it for the government saying, 'deal with this.'"

NDP Leader Andrea Horwath accused Sandals of being AWOL on the file.

"She is still not at the table negotiating seriously with the teachers and I'm hearing parents becoming more and more concerned about the quality of education," she said. "Is there an opportunity over the next couple of months? Absolutely. But that opportunity requires a minister and a government who's serious about getting a settlment."

The legislature has risen for the summer, and MPPs are not scheduled to return to work until Sept. 15, a week after classes resume.

The ETFO began its work-to-rule campaign in early May after eight months of contract negotiations with the province that went nowhere. On Monday, the union ramped up its job action by asking teachers to withdraw from administrative duties.

John Smith, Toronto president of the ETFO, said he believes that parents understand the issues that have sparked the job action.

"Class size, buildings that are falling down, cutbacks to special education, specialist teachers being removed from the school," Smith said.

"This is not about money. They haven't even started talking about money or benefits yet."

With files from CBC Toronto's Jasmin Seputis