TORONTO -- The fragile labour peace between Ontario's Liberals and public school teachers could soon come to an end as two major unions say negotiations have stalled or reached an impasse, with some teachers threatening a strike as early as Monday.

The Elementary Teachers' Federation of Ontario, which applied for conciliation in late March, asked for a "no board report" Monday, signalling that talks with the province are at an impasse. The union would be in a legal strike position 17 days after the report is issued.

"The government and (the Ontario Public School Boards' Association) appear intent on eroding our existing rights and taking us back to the bad old Mike Harris days," the union said in a statement, referring to the former Tory premier whose relations with the unions deteriorated in the '90s.

"They do not appear to be serious about finding a reasonable way to resolve this collective agreement which has been expired now for eight months. Instead, they are provoking a crisis."

It's been three years since the Liberals forced contracts and wage freezes on the teachers through legislation, angering the unions, and the relationship has since slowly improved.

However, as the Liberals try to eliminate a $10.9-billion deficit through measures that include "net zero" increases in contract negotiations, dissent appears to be brewing -- although the teachers say wages are not the only issue.

The Ontario Secondary School Teachers' Federation has threatened to withdraw services at seven school boards, starting with Durham as early as Monday.

Dave Barrowclough, the president of the union local, said if they are close to a deal they won't pull the plug, but Monday is the deadline the union has given.

"It's really up to them as to where we are come Monday," he said. "If we're 98 per cent of the way there, then that might be something that we would change, but we're committed to be here as late as we need to tonight and tomorrow night."

Michael Barrett, chair of the board, said he is optimistic both sides can hammer out a deal over the weekend, but if not, high schools will have to close.

"For the majority of students because we do not have enough supervision without our teaching staff to be able to provide coverage, in the event of a strike we will close our schools and subsequently transportation will be cancelled," he said.

That would send parents of 24,000 students scrambling for alternate arrangements. Parents can stay informed throughout the weekend by checking the board's website, Facebook page or Twitter feed, Barrett said.

This is the first round of negotiations since the province brought in a new bargaining system, with both local and provincial talks.

The high school teachers' union announced Wednesday that it had walked away from the provincial talks, which Education Minister Liz Sandals said probably increased the likelihood of a strike in Durham.

But Sandals suggested it was a bargaining tactic by the powerful teachers' union and predicted they would eventually return to try to reach a new deal.