TORONTO -- The Liberal's plan to sell a majority of Hydro One will drive up electricity rates, cut government revenues and reduce public control over the transmission utility, Ontario's opposition parties warned Monday.

A government-appointed panel that reviewed Crown assets to squeeze out their maximum value for the cash-strapped government concluded the province could raise $9 billion by selling 60 per cent of Hydro One.

The Progressive Conservatives aren't opposed to privatizing Crown assets -- they tried to sell stakes in Hydro One and Ontario Power Generation when they were last in power -- but said government should always maintain majority ownership.

"By selling a majority stake in Hydro One, Ontarians will lose control of this asset, and prices will skyrocket to pay for the last 12 years of this government's mismanagement," said interim PC Leader Jim Wilson.

The New Democrats want Hydro One to stay 100 per cent government owned, and warned giving up 60 per cent of future revenues will only put more upward pressure on Ontario's already high electricity rates.

"Before last week, the premier hadn't even actually talked at all about a plan to sell off the majority of Hydro One," NDP Leader Andrea Horwath said in the legislature. "Does the premier honestly believe that she has a mandate to sell off Hydro One to Bay Street?"

Premier Kathleen Wynne insisted ratepayers would be protected after a Hydro One sale because the Ontario Energy Board will continue to set electricity prices, but the opposition said the OEB has approved huge increases in rates.

The government intends to spend billions on transit and infrastructure projects, and selling a majority of Hydro One will help pay those bills, added Wynne.

"What I believe I have a mandate to do is to invest in the future of this province, to invest in the transit and transportation infrastructure that will allow us to thrive," she told the legislature.

Former Liberal premier Dalton McGuinty warned ratepayers would be hurt when the previous Tory government tried to sell a portion of Hydro One, said Wilson.

"The Liberals agreed with us when we last looked at this and came to the decision that you should always keep a majority share in the company so you have some control," he said.

The opposition parties said the government could be out-voted on any Hydro One decisions by private sector companies who will own 60 per cent of the shares, even though no one owner can hold more than 10 per cent.

"There will be a minimum of six other partners come in to out-vote you, and they're going to want maximum value for their shareholders, which is going to mean higher prices," said Wilson.

The government plans to appoint a special ombudsman for Hydro One, taking away oversight from the provincial ombudsman's office, which is investigating more than 10,000 complaints about the utility's billing practices. The provincial auditor general will also lose oversight of Hydro One six months after the legislation enabling the sale is passed.

"Does the premier really think that, along with less control, Ontarians want less oversight as well," asked Horwath.