Ontario secondary school teachers will be in a legal strike position as of Monday, CTV News has learned.

A strike notice sent from the Ontario Secondary School Teachers' Federation was obtained by CTV Toronto's Naomi Parness on Tuesday.

The notice, addressed to Deputy Minister of Education George Zegarac, states that teachers will begin strike action on Monday, July 20.

All teachers, occasional teachers and support staff will abstain from extra-curricular activities as a result, a source told CTV Toronto. The move will affect students at schools that begin in August, and will extend into the fall if no agreement has been reached between teachers and their employers.

Teachers with the OSSTF in the Rainbow District, Peel Region, and Durham Region School Boards walked out of their classrooms in May, when talks with the local boards broke down. Teachers in the three boards were ordered back to school by the Liberal government, but the back-to-work legislation appears to have done little to quell the looming unrest.

At the same time, the teachers' union walked away from the provincial bargaining table, threatening the possibility of an Ontario-wide strike in the future.

According to Ontario's Minister of Education Liz Sandals, the government is willing to negotiate through the summer months.

"We are prepared to bargain through the summer to ensure that we are all focused on student access come September rather than labour disruptions," Sandals said in a statement emailed to CTV Toronto. “That is why I encourage OSSTF to resume bargaining as soon as possible.”

With files from CTV Toronto's Naomi Parness