The governing Liberals are trying to hide documents related to the costly cancellation of gas plants in Mississauga and Oakville, the NDP charged Friday.

The New Democrats put in a freedom of information request for documents that made reference to "Project Vapour" — a code name the Liberals used in their correspondence about the gas plants.

But the cabinet office denied the existence of any such records, even though some have already been released, said NDP critic Peter Tabuns.

Emails that were among thousands of documents reluctantly released last month by the Liberals include correspondence between high-ranking officials in the premier's office and cabinet office that directly mention Project Vapour.

If they're denying those documents exist, then there may be others that the Liberals are hiding, Tabuns said.

"This is extraordinary stonewalling on the part of the premier," he said. "If it wasn't so Kafka-esque, it would be completely farcical."

But Tabuns stopped short of calling it a lie, saying he couldn't rule out incompetence or the possibility that someone was given orders on how to respond to the request.

Premier Dalton McGuinty should bring back the legislature as soon as possible so the committee that was looking into the gas plants can resume its work, Tabuns said.

The Liberals' initial reluctance to release documents the committee had requested led to a rare contempt of Parliament motion against Energy Minister Chris Bentley.

Many blame the contempt charge for McGuinty's decision to prorogue the legislature when he announced his resignation last month, which killed the motion and planned committee hearings.

He made the announcement three days after the government released a second batch of about 20,000 documents after the premier and his ministers had insisted all relevant records had already been released.

About 36,000 documents were released on Sept. 24 to comply with a Speaker's order.

Bradley Hammond, a spokesman for the premier, said a "thorough" search was conducted into the NDP's request, but "no responsive records were found."

"It's worth noting that not all records are required to be kept," he said in an email.

"Requestors have a right of appeal — they can go to the Information and Privacy Commissioner if they feel the FOI process was not properly followed."

Progressive Conservative Leader Tim Hudak said he doesn't believe that there are no more documents related to the gas plants.

"I don't believe that they found 20,000 additional documents hidden under a rock somewhere either," he said.

"We had to drag that out of them kicking and screaming. This is more evidence of a government that is engaging in an orchestrated cover-up. They don't want people to know the facts of the issue."