Dalton McGuinty's former chief of staff and long-time Liberal campaign director is denying Opposition accusations he was behind decisions to cancel gas plants in Oakville and Mississauga.

Don Guy, one of the most powerful unelected players in Ontario politics, says McGuinty made a commitment as Liberal leader to scrap the partially-built Mississauga plant two weeks before election day in October, 2011.

Testifying at justice committee hearings, Guy said his role was to arrange the public announcement of McGuinty's decision, which was made by Liberal Charles Sousa, now Ontario's Finance Minister.

Guy said he had no discussions with McGuinty about scrapping the Oakville gas plant, and only discussed the Mississauga project with him after the premier had already made his decision to cancel it.

The opposition parties are fuming that they can't ask Guy about emails showing he and other unelected Liberals tried to pressure the Speaker into changing a preliminary finding of contempt against the government.

It came after the government failed to release all documents on the gas plants as requested by a legislative committee.

"Speaker needs to follow up on his prima facie finding and change his mind," Guy wrote last September to senior Liberals including Brendan McGuinty, the premier's brother and a key part of his campaign team.

The Progressive Conservatives and New Democrats accuse the Liberal chair of the committee of trying to block them from getting to the bottom of the gas plant scandal, and say they have a right to ask about all documents they have been given.

They say Premier Kathleen Wynne promised to be open and transparent about the gas plants and to allow the committee to ask any questions its members want.

The opposition parties say the Liberals spent at least $585 million to cancel the gas plants in order to save Liberal seats in the 2011 election.

The auditor general is scheduled to release a report into the actual cost of cancelling the Oakville gas plant at the end of this month, which most observers predict will send the total bill soaring much higher.

The government has said scrapping the Oakville project cost about $40 million, but the Ontario Power Authority puts the figure at closer to $310 million.

The auditor's report on the Mississauga gas plant concluded halting the project in mid construction cost $275 million, far above the $190 million that the Liberals had been claiming.