Last month, Bentley told the legislature all relevant documents were made public when he released 36,000 pages of emails and correspondence on Sept. 24, but the Opposition pounced after so many more documents were released late on Friday.
"The minister should seriously consider tendering his resignation for making these untrue statements to the house," said Deputy PC Leader Christine Elliott.
"However, even if he did this it will not stop our pursuit of the truth of the real cost of the power cost scandal."
The government said the documents showed the cost of cancelling the two energy projects was $230 million, while the opposition parties had said it was closer to $650 million, a figure Elliott revised to $1 billion after a quick look at the new documents.
"There is some suggestion in the documents that they’re talking about $1 billion plus," she said.
"We haven’t had a chance to go through all of the documents yet, but it’s certainly mentioned in those we’ve seen so far."
The New Democrats said it was clear the Liberals could not be trusted and their credibility has been greatly diminished.
"Even though they’re diminishing its importance, the important point is that we said that there were more documents, they claimed there weren’t, and all of a sudden we find that there are," said NDP critic Rosario Marchese.
"They have to wear this. They do have to deal with the fact that people just don’t believe them any more."
Bentley said he had been advised by the OPA and by ministry officials "that all responsive records" were submitted in the original 36,000 pages released last month, and accepted responsibility for the fact thousands more documents had been found, but did not respond to the call for his resignation.
"Of course it’s frustrating and challenging," he said in an interview.
"I know the officials were acting in good faith. We all wanted all of the documents to go over with the 36,000, and all believed that they had been."
All legislative business ground to a halt for a week last month while members debated a contempt motion against Bentley, which was triggered by the government's reluctance to release the gas plant documents to a committee.
The Tories said they would pursue a second contempt motion, this time including Premier Dalton McGuinty and government house leader John Milloy, who also told the legislature that all relevant documents had been released.
"At one point an apology and true contrition could have solved this scandalous debacle," said Elliott.
"Try as they may to blame this on their officials as a bureaucratic mix-up, what we are really witnessing here is a political cover-up."
Both the Tories and New Democrats accuse the Liberals of cancelling the gas-fired generating stations in Oakville and Mississauga to save Liberal seats in the area, and say the government is underestimating the true cost of its decisions to taxpayers.
The legislature's finance committee next week will start its consideration of the original contempt motion against Bentley, and the cost of cancelling the gas plants, and is scheduled to report back to the legislature by late next month.
No elected member of the Ontario legislature has ever been found in contempt of Parliament, which McGuinty warned could have serious implications for Bentley.