The Ontario government came under renewed attack from opposition members Thursday after the Liberals revealed that dozens of unreleased documents relating to a pair of cancelled gas plants had been discovered.

Energy Minister Bob Chiarelli informed the legislature on Thursday morning that he had been informed the previous evening of the existence of additional documents about the cancelled gas plants that had not been released.

"The documents in question are being compiled as I speak and will be tabled with the clerk at the legislative assembly as soon as possible this afternoon," Chiarelli said.

The Liberals initially released a batch of documents in September and told the legislature that they had all been released. A month later, another 20,000 pages of documents were found.

Executives from the Ontario Power Authority spoke to members of the media on Thursday afternoon, attempting to explain the reasons why the latest batch of documents had not previously been accounted for.

Jim Hinds, the chair of the OPA’s board of directors, said that mistakes were made when trying to locate all of the documents last fall.

"Today we disclosed an additional 67 documents to the clerk of the house relating to the Mississauga and Oakville gas plants," he told reporters at Queen’s Park.

"This additional disclosure has arisen due to inadvertence on the part of the OPA."

Hinds said that the OPA found that it had failed to search for documents under "certain project code words," when it was searching for them last fall.

"We are in the business of producing electricity, not producing documents," Hinds said, noting that this was "the first large-scale document search" the OPA had ever undertaken.

The Canadian Press reports that the latest batch of documents totals about 600 pages.

Opposition pounces on government

The leaders of both opposition parties were quick to slam the government following the revelation from the energy minister.

Progressive Conservative Leader Tim Hudak said he wanted to express his "extreme disappointment … that after only three days in this house this kind of trick, this kind of tactic, shows how much this government looks like the Dalton McGuinty government."

McGuinty's resignation last October came just hours before committee hearings were to begin on a contempt motion that related to the Liberal government's withholding of documents related to the gas plants.

New Democrat Leader Andrea Horwath asked Wynne on Thursday when she became aware of the existence of the additional documents.

Wynne said that she found out from the energy minister on Wednesday evening, admitting that it was "disappointing" that the government was unaware of the additional documents.

NDP Leader Andrea Horwath demanded an explanation from the premier on how the government could find out again that there are outstanding documents on the cancelled gas plants that have still not been released. (CBC)

The NDP leader then suggested the latest identification of new documents was part of "an ongoing process of obfuscation of the facts by this government."

The speaker then asked Horwath to withdraw her remark, which she did.

"Speaker, the bottom line is this: The energy minister announced just a moment ago that for a second time, a government agency has uncovered yet more documents on the cancelled gas plants. Documents that this government has insisted repeatedly did not exist," Horwath said.

"They didn’t exist the first time — apparently they didn’t exist this time either. Does the premier have any explanation whatsoever for the people of this province or any justification on how this kind of thing can happen in a democratic society like Ontario?"

Wynne said it was "unfortunate" that not all of the documents had been released before this, but the remainder "are coming forward and that’s as it should be."

The government says the cost of scrapping the gas plants is $230 million. But the opposition says the price tag is far higher.

The controversy over the cancelled gas plants has dogged the Liberals for months and has flared up again in the newly started parliamentary session.

With files from The Canadian Press