The Ontario government has introduced legislation that would prevent a strike or lockout at one of the province's major power utilities, a move it says is necessary to avoid power outages over the holidays.

Labour Minister Laurie Scott said that if passed, the bill would send the dispute between the Power Workers' Union and Ontario Power Generation to arbitration.

The Progressive Conservatives reconvened the legislature on Monday — just over a week after lawmakers rose for their winter break — to table the bill that would stop job action at the utility.

The move has been criticized by the official Opposition, which said the province didn't even wait for the strike to begin before threatening to force workers back on the job.

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NDP Leader Andrea Horwath said the province had other options available, but "went straight to the biggest hammer available, which is back-to-work legislation."

Howarth said her party will not support the legislation, but she expects it to pass by Thursday due to the PC's majority.

Green party Leader Mike Schreiner, meanwhile, said he looked forward to reviewing the details of the legislation and hoped it would respect the bargaining process.

"It is important that this government resists the urge to punish workers as they have done with other legislation this fall," he said in a statement.

Government warns power could go down during holiday season

The emergency session was announced in a statement Friday evening by PC House Leader Todd Smith. The government has said a strike could cause power outages in as little as a week.

Ontario NDP Leader Andrea Horwath told reporters the government's decision to preemptively block the strike was plain wrong. (Frank Gunn/Canadian Press)

The notice of a strike also came on Friday, a day after members of the Power Workers' Union rejected a contract offer from OPG.

OPG spokesperson Neal Kelly told CBC News that means workers could start a days-long process of shutting down nuclear power plants, before potentially launching a strike on Jan. 4, 2019.

The organization that manages Ontario's power system said in a statement Friday that a strike at OPG would put the system's reliability at risk.

"The shutdown of OPG's nuclear and hydroelectric facilities could occur in approximately three weeks. At that point Ontario would not have the generation needed to meet consumer demand and customers would begin losing power," the Independent Electricity System Operator said in a statement.

"The IESO will take every action available to delay and mitigate the impact... However, these actions will not be enough to prevent significant losses of power."

The union, which has been without a collective bargaining agreement since March 31, said Friday that OPG's final offer was rejected by a nearly 60 per cent vote of its membership.

The main sticking point in talks is OPG's refusal to grant over 300 so-called "term" workers the same rights as full-time employees at the Darlington and Pickering Nuclear Plants, the union said.

The union represents over 16,000 workers in Ontario's energy sector, including about 6,000 OPG employees.