While Ontario's spending watchdog is slamming the Wynne government for allegedly trying to hide the true cost of its hydro price cuts, she's also criticizing the Liberals for trying to hide documents from her investigation.

Auditor General Bonnie Lysyk said the Ministry of Energy has still not provided all the emails she requested back in May to prepare her special report the government's Fair Hydro Plan.

The Progressive Conservatives are now asking Ontario's top public servant to ensure that all relevant documents and emails are saved.

"We must insist that all records related to this matter ... be preserved," said PC leader Patrick Brown's chief of staff, Alykhan Velshi, in a letter to Head of the Public Service Steve Orsini on Wednesday. A copy of the letter was obtained by CBC News.

Brown will call for an investigation Thursday, according to officials in his party.

The Liberals insist they are not hiding anything.

Auditor General Bonnie Lysyk says the Liberal government set up its Fair Hydro Plan impropely 'to keep deficits and an increase in net debt from showing up on the province's books.' (Mike Crawley/CBC)

"Over 13,000 emails have already been brought forward to the Auditor General's office," Energy Minister Glenn Thibeault said Wednesday during question period. "We're going to continue to work and provide her with all of the emails that she asked for."

Thibeault later told reporters that ministry staff expect to hand over the remaining emails to the auditor in the coming weeks.

Government hired law firm to sift emails

Lysyk's report said she received the documents she requested from all government departments except the Ministry of Energy.

"The Ministry of Energy signed a contract, with a retainer of $500,000, to receive help from a law firm to provide search services and to compile emails before providing them to us," writes the auditor in the report, released Tuesday.

"At the time we completed this Special Report, the Ministry had still not provided us with all of its emails, which we requested on May 31, said Lysyk.

Thibeault says the law firm had to be hired because an initial search suggested up to two million emails were relevant to the auditor's probe.

"Those two million emails then were reviewed by the firm to which we've paid approximately $40,000; we will not be going over $60,000 on this," said Thibeault in question period. "That firm then identified those 145,000 emails, which the Ministry of Energy is now identifying and releasing.