TORONTO -- Ontario's Progressive Conservatives plan to ask the auditor general to look into $3.74 million the government paid unions representing teachers and education workers over the past three rounds of bargaining.

Tory MPP Lisa MacLeod will introduce a notice of motion Wednesday at the public accounts committee, of which she is vice-chair, asking the auditor general to investigate those payments as well as $4.6 million that is being paid to school boards for their bargaining costs.

But the Liberals have a majority on the committee, which means they could easily block the motion.

MacLeod, though, is hopeful because the Liberals previously agreed to a motion asking Auditor General Bonnie Lysyk for a Pan Am Games audit.

"A sum of money this large going undocumented to some public-sector unions who ran attack ads -- it doesn't look good," said MacLeod, referring to anti-Tory advertising during the last provincial election.

"I think it would be important that the auditor review those numbers and make sure the money wasn't misappropriated, although I believe it has been."

Education Minister Liz Sandals has defended the payments as being necessary because the transition to a new bargaining system made this round quite lengthy.

And the ministry has said that it was appropriate to make similar payments in 2008 and 2012 to three education unions because it involved voluntary discussions that were a precursor to the new system.

Sandals said she is not at all concerned about a possible auditor general investigation.

In the last provincial election, the Ontario Secondary School Teachers' Federation, the Ontario English Catholic Teachers' Association and the Elementary Teachers' Federation of Ontario put $250,000 each toward third-party advertising from the Working Families coalition, a group of unions that comes together each election to run anti-Tory ads.

ETFO, which is still in negotiations and has said it won't take government money for bargaining costs, spent another $1.3 million on election advertising in 2014. OECTA spent a further $2.2 million and OSSTF spent $386,000.

The committee would vote on MacLeod's motion next Wednesday. She is concerned the practice is more widespread than the government is saying.

"We know some unions have indicated it hasn't, but we have over 4,000 collective agreements" in the broader public sector, she said. "Can you imagine if each time we sat down for a collective agreement we gave the union we're negotiating with one million dollars?"