TORONTO -- The threat of a teachers' strike grew larger Wednesday after the union representing public high school teachers walked away from provincial contract talks.

The first school board that could be hit by a strike is in Durham region, east of Toronto, and those teachers will be in a legal strike position by Monday, warned Education Minister Liz Sandals.

"Certainly the fact that they have suspended the negotiations on Wednesday means that the possibility of a strike in Durham on Monday has probably increased," Sandals told reporters. "I think it would be only prudent for parents to be paying attention."

There are both local and provincial rounds of negotiations between teachers' unions, school boards and the Ontario government. It was the provincial talks with the Ontario Public School Boards Association that the OSSTF announced it was suspending "until the employer gets serious."

The union did not immediately respond to requests for comment on its statement.

Sandals said she'd seen this kind of withdrawal from negotiations before, suggesting it was a bargaining tactic by the powerful teachers' union and predicted they would eventually return to try and reach a new deal.

"I am not taking it lightly," she insisted. "But I also don't think when you have a situation where people indicate they are suspending negotiations that we should take it as that's the end of negotiations."

Earlier this month, the OSSTF threatened to withdraw services at seven boards: Peel, Durham, Halton, Ottawa-Carleton, Waterloo, Rainbow in Sudbury and Lakehead in Thunder Bay. Sandals was much more optimistic then about progress being made in negotiations, but wouldn't say what new stumbling blocks emerged.

"I'm not going to get into individual issues, but it's the nature of negotiations," said Sandals. "You're dealing with one set of issues and you make some progress, but you turn to a different set of issues and you make less progress."

The Liberal government insisted there will be no funding for wage increases for teachers or any public sector workers until it eliminates a $10.9-billion deficit.

"We've said all along that this is a net zero round of bargaining and we remain committed to that," said Sandals. "That's why it's a difficult round of negotiations."

The Opposition said it wants to make sure the school year is protected for students who could be hit with teachers' strikes, and accused the Liberals of squandering money during good times so they can no longer afford to give educators raises.

"The reality is they have no money," said Progressive Conservative education critic Garfield Dunlop. "In the end they may have to some up with some additional money to borrow on top of our debt."

The New Democrats said they weren't surprised to hear the high school teachers' union suspended talks, given all the cuts the Liberals have made to education.

"I've been hearing the frustrations for months about the slowness in the process of getting the central issues dealt with at the bargaining table," said NDP Leader Andrea Horwath.