TORONTO -- The Ontario government introduced legislation Monday that would prevent a strike or lockout at one of the province's major power utilities, a move its said was 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.

"This will prevent the effective shutdown of as much as half of Ontario's electricity system," she said.

The Progressive Conservatives reconvened the legislature 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, who say the province didn't even wait for the strike to begin before threatening to force workers back on the job.

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

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.

Labour groups denounced the bill, saying Ontario residents should be concerned at the speed and manner in which the government acted.

"These workers have not even gone on strike yet and the government is proposing back-to-work legislation," Chris Buckley, president of the Ontario Federation of Labour, said in a statement.

"This time it is power workers but there is no telling who will be on the receiving end of these rash actions next."

The emergency session was announced in a statement Friday evening by Government House Leader Todd Smith. The notice of a strike also came on Friday, a day after members of the Power Workers' Union rejected a contract offer from OPG, putting them in a legal strike position.

The organization that manages Ontario's power system has said 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 Friday.

The government has said a strike could cause power outages in as little as a week.

The union, which has been without a collective bargaining agreement since March 31, has said 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 roughly 6,000 at OPG.