TORONTO -- The three Ontario teachers' unions promised $2.5 million by the Ontario government to help them cover the cost of contract negotiations will have to provide receipts.

Premier Kathleen Wynne surprised the legislature Wednesday by saying the teachers' unions will have to show the government proof of their expenditures during the new, long negotiating process introduced by the Liberals for this round of bargaining.

"Before that money flows, there will be an accounting of how that money is used and what that money is for and what the costs were," said Wynne. "It's part of the agreement that it hasn't flowed, and the teachers' unions will provide an accounting of their costs."

Education Minister Liz Sandals has repeatedly said the government didn't need to see receipts from the teachers' unions because she knew how much hotels and pizzas cost.

"You're asking me if I have receipts and invoices; no, I don't," Sandals said last week. "You don't need to see every bill when you're doing an estimate of costs."

Those comments by Sandals sparked outrage among the Progressive Conservatives, who claimed the teachers' unions took the money from the Liberal government and used it to fund anti-PC attack ads during the 2014 Ontario election. They demanded the government ask for receipts from the unions to justify the payments for their negotiating costs.

The Tories weren't happy with Wynne's new version of the payouts plan Wednesday, and moved a motion at the Liberal-dominated public accounts committee to have the auditor general investigate the payments to the teachers' unions.

"If the government has nothing to hide, if everything is by the book, then why not let the auditor general review these expenses," asked deputy PC leader Steve Clark.

The Progressive Conservatives complained that Wynne's story about the payouts keeps changing, and said they still want to know where the money came from.

Wynne said there were savings elsewhere in the contracts with unions representing high school teachers, English Catholic teachers and French teachers to offset the government's move to pick up their costs for the negotiations.

"The funds did not come out of the classroom," she said.

The Tories want the auditor to look into a total of $3.74 million the government paid unions representing teachers and education workers over the past three rounds of bargaining going back to 2008.

Wynne said the auditor general is free to look at anything she likes, but wouldn't say if the Liberals on the committee would agree to a full audit of the payments to the unions.

The government admits it doesn't pay any of the unions representing its direct employees any additional money to cover their costs for negotiations.

Meanwhile, the NDP demanded Sandals resign for the government's failure to reach an agreement with Ontario's elementary teachers, who stepped up their work-to-rule campaign Wednesday by withdrawing from extracurricular activities.

"This government continues to cause chaos in our schools and is forcing students and families to pay the price for a minister who can't get the job done," said NDP education critic Lisa Gretzky. "The minister of education has lost all credibility and needs to go."