The Canadian Union of Public Employees said Wednesday that its lawsuit against the Ontario premier and two Liberal cabinet ministers over the sale of Hydro One is finally headed to court.

CUPE Ontario president Fred Hahn said the suit, officially filed on Tuesday, is aimed at stopping the sale of any more shares in the giant electricity transmission utility before private owners have control of its board.

"Today we still own a majority of Hydro One and there is still accountability to our government," said Hahn. "The minute we lose majority control, decisions about the electrical system will be controlled by a corporate board whose sole interest is in raising profit, not the interests of the people."

The government has already sold about 30 per cent of the shares in Hydro One, and plans to sell another 30 per cent to raise a total of $9 billion to pay down debt and to fund public transit and infrastructure projects.

The province has raised about $3.8 billion so far from selling shares, but also gained another $3 billion from a deferred tax asset benefit, a special dividend and payment-in-lieu of taxes as part of the privatization process.

The ramifications of privatization will last decades because the province is giving up most of the hundreds of millions of dollars in guaranteed revenue Hydro One turns over to the government each year, added Hahn.

"If this is allowed to happen, the negative impacts will be felt for generations to come," he warned.

In September, CUPE served the Ministry of the Attorney General with a notice of intent to sue Premier Kathleen Wynne, Finance Minister Charles Sousa and former Energy Minister Bob Chiarelli for misfeasance.

The union claims the Liberals inappropriately mixed government and party business by holding fundraisers with cabinet ministers, including one $7,500-a-ticket event with Sousa and Chiarelli that was attended by bankers who profited from the privatization of Hydro One.

Speaking at a transit announcement in Toronto, Wynne said Wednesday the integrity commissioner confirmed there was no wrongdoing with the cabinet ministers attending the fundraiser.

"We have at every juncture checked what we're doing, and the integrity commissioner has already ruled on the issue that is before the court," she said.

"I can't comment on that court case, but what I can say is that broadening the ownership of Hydro One has everything to do with investing in the infrastructure projects that we're talking about here today."

Integrity Commissioner J. David Wake found that Sousa and Chiarelli may have benefited politically by attending the fundraiser with bankers involved with the sale of Hydro One, but they didn't contravene the Members' Integrity Act.

However, he also said the legislature should consider clarifying the law to include the apparent conflicts of interest, not just actual ones.

Chiarelli insisted there was no specific government business discussed at the fundraiser, which he said was held after the initial public offering of Hydro One shares.

"There could be discussions about high level issues, where's infrastructure going, where's energy going, a general dialogue between the ministry and stakeholders that we have all the time," said Chiarelli, now the minister of infrastructure.

The government followed the integrity commissioner's advice and tightened fundraising rules to prevent cabinet ministers from holding events with lobbyists looking to do business with their ministry, added Chiarelli.

The Progressive Conservatives and New Democrats urged the government to halt the sale of Hydro One, at least while the CUPE suit is dealt with in court.

"If the stories about the cash for access, about how the banking syndicate that did the fire sale had this huge fundraiser for the Liberal party wasn't enough, then maybe this lawsuit will finally give the premier another opportunity to do the right thing and halt the sale of Hydro One," said PC Leader Patrick Brown.

Hydro One, which also serves as a local electricity distribution company for 1.3 million homes in remote and rural parts of Ontario, announced Wednesday it would restore service for the winter to 1,400 customers who'd been cut off for not paying their bills.