TORONTO -- Ontario's finance minister said the province will have to make sacrifices as it grapples with a newly revised $15-billion deficit, a message critics predicted would pave the way for significant cuts to government services.

In a speech to the Economic Club in Toronto on Friday, Vic Fedeli said the province had chosen to adopt the accounting practices used by the auditor general in reviewing the recently defeated Liberal government's budget and projections, and found greater deficits than had been reported.

"The hole is deep and it will require everyone to make sacrifices without exception," Fedeli said in the speech, his first major address since taking on the finance portfolio. "It will require a unity of purpose, a clear vision and a lot of hard work."

As a result of the new Progressive Conservative government's adjusted take on the province's books, an independent commission tasked with examining Ontario's finances concluded the Liberals ran a $3.7 billion deficit in the last fiscal year rather than balancing the budget as claimed, Fedeli said.

The commission also found the Liberals had overestimated their revenues for this fiscal year, reduced a reserve fund by $300 million and claimed $1.4 billion in cost-cutting measures that weren't spelled out.

Once those were factored in, the projected deficit for 2018-19 rose to $15 billion from the $11.7 billion predicted by the auditor general, the government said.

Fedeli would not give a timeline for getting the province back in the black, though the Progressive Conservatives promised during the election campaign that they would return to balance by the end of their mandate.

"We will return to a balanced budget on a timetable that is reasonable, modest and pragmatic -- but we will return to balance in Ontario," he said.

Critics warned the commission and its findings would be used to justify sweeping cuts, noting Premier Doug Ford has vowed to find billions in so-called "efficiencies."

The Liberals accused the government of using inflated numbers for political gain, saying the figures cited by the commission were known long before the election.

"It's a context for cuts," Interim leader John Fraser said. "They're going to be deep."

NDP finance critic Sandy Shaw called Fedeli's speech an "act of political theatre," and noted the Liberals behaved similarly when they took over from the Progressive Conservatives in 2003.

"They aren't going to deliver relief. They're going to cut and privatize," she said.

Green Party leader Mike Schreiner said that while the commission paints a bleak picture of Ontario's finances, that should not be used to bring in sweeping austerity measures.

"Finding efficiencies on the backs of our most vulnerable citizens is wrong. And it will only lead to more costs down the road," he said in a statement.

Some labour groups also expressed alarm at Friday's announcement, saying Ontario residents would suffer if services are cut or privatized.

Asked whether there would be service cuts or job losses, Fedeli said the premier had been clear about targeting only efficiencies.

Treasury Board President Peter Bethlenfalvy said the government would work with the broader public service to find ways to move forward without threatening the jobs of frontline workers.

"This is not about cuts," he said. "It's about transforming the way government runs its businesses, about modernizing the government services."

Paul LeBane, vice president of public finance with the independent credit ratings agency DBRS, said that while the additional deficit beyond the auditor general's tally was a little surprising, "from a credit perspective, not much has changed."

"It doesn't really change the province's borrowing requirements, it doesn't really change their cash position all that much, maybe they'll borrow a little bit more to have a little bit more in contingency, in reserve," he said.

What's more, the deficit projection for 2018-19 appears based on the budget presented by the Liberals and doesn't seem to factor in the new government's policies or priorities, LeBane said. "That $15 billion will have to change as the year progresses," he said.

The Progressive Conservative government announced the independent commission in July and tasked it with probing the Liberal regime's accounting methods surrounding a pair of teacher pension plans and the province's Fair Hydro Plan.

Those accounting practices had led to a two-year fight with Ontario's auditor general, who said in April that the Liberals understated their deficits by billions.

Bonnie Lysyk suggested that the $6.7-billion deficit projected by the Liberals for 2018-2019 would be $11.7 billion instead, and the projected $6.5 billion for 2020-2021 would actually be $12.5 billion.

The Conservatives have also ordered a line-by-line audit of government spending, which is expected to be finished in the coming weeks.