TORONTO -- Ontario's public elementary schools will be open Monday, but teachers will not perform some administrative duties as part of what they're calling the first phase of a province-wide strike.

Extracurricular activities and field trips will continue for now, there will be no standardized tests, no comments will be added to report cards beyond the marks, and teachers won't participate in any meetings or professional development related to Ministry of Education initiatives.

The president of the Elementary Teachers' Federation of Ontario left open the door to escalating the job action.

"This strike action is incremental in nature," Sam Hammond said Friday. "It will continue in its current form until (the government and school boards') demands are withdrawn from the bargaining table or ETFO deems that further actions are required."

He would not say what a second phase could entail.

The union told its members about the work-to-rule action in a memo earlier this week, but refused to confirm it publicly until Friday at 2 p.m. If teachers move into a second phase they will give parents more than two days' notice, Hammond said.

Hammond said his members will not allow school boards to increase class sizes, but the Ontario Public School Boards Association said it's incorrect to suggest it is advocating for that.

The teachers' union is demanding that all of the OPSBA proposals be withdrawn from the table, which is unreasonable, said its president Michael Barrett.

"The concept of negotiation is to be able to put positions on the table then bargain...in order to be able to come to a compromise," he said. "Withdrawing all our items on the table to only be concerned with items they have on is not bargaining."

Education Minister Liz Sandals said in a statement that she is disappointed with the ETFO decision, but she is "encouraged" that students will remain in the classrooms.

The elementary strike comes as more than 70,000 high school students in the province sit home because teachers in the Toronto-area boards of Peel and Durham, as well as Sudbury, have walked off the job.

This is the first round of negotiations for both high school and elementary teachers since the province brought in a new bargaining system with both local and provincial talks. It's also the first time the OPSBA has participated in the central negotiations and Hammond said it has "recklessly demanded numerous concessions and utterly disrespected our members and their agreements."

Hammond singled out teacher preparation time, supervision, ability to exercise professional judgment and fair and equitable hiring practices as some of the key areas in which OPSBA and the government are making demands.

"We will not allow others to dictate how teachers and occasional teachers spend their preparation time, which would interfere with their ability to plan lessons and prepare specialized plans for students, nor will we allow teachers to be micromanaged," he said.

Except for class sizes, Barrett didn't dispute many of the areas in which OPSBA has made proposals, but he said the suggested changes are ones they believe would actually strengthen the education system.