The minority Liberals and the Conservatives are expected to team up in the legislature to pass the anti-strike bill, which has angered unions and civil libertarians.
Unions representing most teachers say it violates their constitutional rights and have vowed to fight it in court.
The Liberals brought back the legislature early to get it passed before Sept. 1, saying the province couldn't afford the rollover of old contracts.
But since the proposed legislation is retroactive to that date, it would claw back any pay hikes or benefits once it becomes law.
The bill would force new contracts on the majority of teachers and education workers in the province to help eliminate Ontario's $15-billion deficit.
It's based on an agreement the province reached with English Catholic and francophone teachers, including three unpaid days off in the second year and cutting sick days in half to 10 a year.
But the two biggest unions representing elementary and high school teachers have rejected it and vow to fight it all the way to the Supreme Court of Canada.
The Canadian Civil Liberties Association has also complained about the bill, saying it's unconstitutional and undemocratic.
Education Minister Laurel Broten says she can't stop anyone from challenging the legislation, but she believes it will stand up in court.
"If this bill passes — and we are hopeful that it will — and it is challenged in court, we will defend it as being constitutional, and we take the position that it's reasonable and justified under the circumstances," she said.
The New Democrats, who oppose the bill, say the legislation is unnecessary since the teachers never threatened to go on strike.
The government is taking a reckless path that will end up costing taxpayers millions of dollars, said NDP Leader Andrea Horwath.
The Liberals claimed they were fast-tracking the bill to ensure the start of the school year was free from labour disruption, she said.
"What they've done is pretending on the one hand that they're bringing peace to the school year, they in fact created the opposite, they created a whole bunch of turmoil," Horwath said.
"That's not helpful at all and kids are the ones being caught in the crossfire. It's the students who are going to feel the anxiety of uncertainty."
The Liberals may have paid the price for the legislation in two important byelections last week.
The Liberals held on to the riding of Vaughan, but came in third in Kitchener-Waterloo, denying them a majority government.
The NDP picked up the riding instead and got a lot of help from the unions in getting out the vote.
Debate on the legislation was limited last week thanks to the Tories and Liberals, with public hearings that lasted just a few hours.