Just when you thought things were settled between Ontario's teachers unions and the province, the rivals are facing off once again — this time, in court.

Five unions are challenging the constitutionality of Bill 115, the "Putting Students First Act." The controversial legislation imposed contracts on education unions and banned them from striking, when collective bargaining stalled in 2012.

The Bill not only required ETFO to "bargain" with a metaphorical gun to its head, it dictated the terms of the bargain. ETFO legal submission

The hearing begins in Ontario Superior Court at Toronto's Osgoode Hall this morning and is scheduled to last all week.

The results of the case will have strong implications for the power of governments in Canada to dictate the terms of union contracts and to take away the right to strike.

The Ontario Public Service Employees Union (OPSEU) is leading the Charter challenge, joined by the Elementary Teachers Federation of Ontario (ETFO), the Ontario Secondary School Teachers Federation (OSSTF) and two other unions.

OPSEU's submission to the court says provisions in Bill 115 violate the freedom of association enshrined in the Canadian Charter of Rights and Freedoms.

"Collective bargaining is firmly entrenched as a full-fledged Charter right," OPSEU's lawyers write in their submission. They argue the Charter prevents "powerful entities, such as employers and government, from running roughshod over the interests of employees."

The government argues that the Charter protection of collective bargaining does not stop it from imposing wage restraint.

"This case is about what constitutionally permissible options are available to government when it faces a looming fiscal challenge," lawyers for the province write in their submission to the court.

The government's lawyers argue that Bill 115 does not violate the Charter because the contracts were imposed only "after many months of good-faith consultation."

Bill 115 was imposed by the government of former premier Dalton McGuinty. It was repealed not long before Kathleen Wynne won the Liberal leadership. (Canadian Press) Bill 115 was introduced by the Liberal government of then-premier Dalton McGuinty in late August 2012, just days before the school year began.

"The Bill not only required ETFO to "bargain" with a metaphorical gun to its head, it dictated the terms of the bargain," ETFO lawyers write in their submission to the Ontario Superior Court.

Four months later, amid the growing threat of strikes, the government used the legislation to impose contracts on education unions that froze salaries, stopped teachers from moving up the salary grid as they gained seniority, and ended hefty payouts for unused sick days. The imposed contracts banned strikes until 2014.

Immediately after the "Putting Students First Act" was used to impose the contracts, the legislature repealed it. Mere days later, Kathleen Wynne won the Liberal leadership convention and became premier.

The unions say it is necessary to challenge the bill retroactively to prevent governments from doing something similar in future.

If the court agrees the union members' charter rights were violated, it will have to decide whether the violation was "justified in a free and democratic society," whether the government's goal with the legislation was important enough to override a constitutional right.

A decision is not expected for weeks, and whatever the ruling at the Ontario Superior Court level, it's likely to be appealed. Ultimately, if they win, the unions are asking for compensation, including lost wages.