More than one million students across Ontario face a day of cancelled school in the coming week because of teachers' strikes, but the government of Premier Doug Ford is not using legislation to stop the walkouts — at least not yet.

Legislating teachers back to work is "the last step," Ford said this week when he took questions from reporters at Queen's Park. "What we really want to do is get a deal."

How much labour disruption would it take for the government to legislate an end to the strikes? When I asked Education Minister Stephen Lecce, he said that's not his focus right now, and said negotiated agreements are the "best option for all the parties."

What neither Progressive Conservative politician mentioned: imposing back-to-work legislation now would not likely stand up in court.

To defend such legislation, the government must persuade a court that its actions have a "pressing and substantial purpose." That's the legal test established by the Supreme Court of Canada to justify violating the right to free collective bargaining enshrined in the Charter of Rights and Freedoms.

'We'll listen to families in the coming days and weeks about the impacts' of teachers' strikes, Education Minister Stephen Lecce said on Wednesday. 'But, for now, the focus is on getting a voluntary settlement.' (Kate Bueckert/CBC)

A day of school lost here and there to rotating strikes almost certainly doesn't meet that bar, according to legal experts.

"There's a difference between a pressing and substantial purpose and an inconvenience to the public," said Kevin Banks, director of Queen's University's Centre for Law in the Contemporary Workplace.

"If the government's reasons [for back-to-work legislation] have to do with inconvenience, then it may well be too early," Banks said in an interview. "If things get to the point where the school year is in jeopardy, I suspect that there's a good chance a court would say, 'Yes, that is a pressing and substantial purpose.'"

This is one of the key reasons why Ontario teachers unions are strategically choosing to hold one-day strikes. They fear a full-blown indefinite walkout would soon prompt the government to reach for the hammer of back-to-work legislation.

The unions figure these short, rotating work stoppages are their best bet to dissuade the government from making such a move, or to win a legal battle if it comes to that.

The Ontario English Catholic Teachers' Association is set for a province-wide strike on Tuesday. It will be the union's first strike since 2003. (CBC)

Most recently in post-secondary education, it took weeks of strikes rather than days before previous Ontario governments resorted to legislation.

The 2018 strike at York University lasted two months before Kathleen Wynne's Liberal government introduced a back-to-work bill. It died when Queen's Park was dissolved for the election campaign, then the new Ford government moved to end the strike with its first piece of legislation.

In 2017, a faculty strike closed the province's 24 colleges, cancelling courses for hundreds of thousands of students for five weeks before the Wynne government legislated an end to the dispute.

That back-to-work bill might not have withstood a legal challenge had the government brought it in sooner, Minister of Advanced Education Deb Matthews told reporters at the time.

"You have to have a very, very good rationale, that the academic year [must be] in jeopardy," Matthews said, explaining that the Supreme Court set a "very high bar."

The one-day strikes planned this week will close schools for more than one million Ontario students. (Francis Ferland/CBC)

In the 1990s in Ontario, it typically took about five weeks into an education strike before an arm's-length body called the Education Relations Commission ruled that a labour dispute was putting the school year in jeopardy, giving the government the political go-ahead for back-to-work legislation.

Mike Harris's Progressive Conservative government pre-empted that process in 1998, moving to legislate when some 200,000 students in eight boards had been out of class because of labour disputes for just two weeks at the beginning of the school year.

In 1997, the Harris government tried to use the courts to stop a province-wide strike just as it began. A judge declined to give the province the emergency injunction it sought. A two-week strike ensued, ending when teachers returned to work voluntarily.

If the Ford government eventually chooses back-to-work legislation, it faces another key strategic decision: how to determine the terms of the contract? Does the government impose a contract or send the dispute to binding arbitration?

An arbitrator might give the teachers a contract that exceeds what the government wants to spend, either in a wage increase or class size provisions, issues at the centre of the current round of stalled negotiations.

Legal experts say it's too early in the teachers' strikes for back-to-work legislation to stand up in court. (Michael Wilson/CBC)

An imposed contract would itself undoubtedly face a legal challenge. The government would again have to prove it is meeting that legal test of a "pressing and substantial purpose" to justify violating the right to free collective bargaining.

Its likely argument: the province is in a serious fiscal imbalance and can't afford to give the teachers what they're asking for.

"I'm not entirely sure that that argument would fly, but it's at least a plausible argument," said Banks.

It's an argument that will be put to the test in an upcoming legal challenge against the government's three-year cap on public sector wage increases at one per cent annually.