Ontario Liberal Leader Kathleen Wynne questions the NDP's platform at the Finishing Trades Institute of Ontario in Toronto on Monday, May 14, 2018. THE CANADIAN PRESS/Chris Young

In a clear sign that the NDP are the party to beat, the Liberal campaign issued a take down of the New Democrat’s platform.

On day six of the election campaign the third-place Liberals held a technical briefing to say the NDP made a mistake in their platform costing and are missing at least $3 billion in program spending.

According to the Liberals, the NDP erred in using 2017 budget spending as their base for new investments without accounting for the in-year new spending that the government announced between last year’s March budget and this year’s.

“I think this is about the NDP making a mistake,” Premier Kathleen Wynne told reporters.

The Monday morning salvo follows a string of attacks the NDP have received from both the Liberals and Progressive Conservatives since Thursday. The most recent polls show the Tories are the frontrunners, but that the NDP have surpassed the Liberals and enter week two of the campaign with some momentum.

[READ MORE: Ford slams NDP’s ‘extremist environmental friends’]

Voters head to the polls on June 7.

The Liberals say the NDP likely were attempting to only remove new spending announced in the 2018 budget, but overcorrected and removed previous spending commitments.

The NDP are rejecting the Liberals’ assertions.

At stake, according to the Liberals, are multi-year programs that were announced after last year’s March budget.

The party pointed to spending, such as new funding for apprenticeship programs, cannabis legalization, services for people with autism, and funding for Ontario’s strategy to combat the opioid crisis.

She left the harshest criticisms to her cabinet colleagues who said the NDP platform is “built on a foundational error” and is a “mess.”

The NDP had former parliamentary budget officer (now the President of the Institute of Fiscal Studies and Democracy) Kevin Page vet its platform. A letter signed by Page says the institute “reviewed the broad economic and fiscal assumptions” and the costing of new spending promises that totalled more than $1 billion.

But the Liberals face their own unanswered questions about numbers. The premier and her cabinet have repeatedly dismissed findings from the auditor general that their deficit for the current year is off by $5 billion.

Bonnie Lysyk’s pre-election report said the Liberal’s deficit should be close to double what’s projected for this year and the next two.

Wynne rejected the comparison saying “that’s not what this is about.”

[READ MORE: ‘I’m taking care of our own first,’ Ford says on immigration]

The NDP released a statement saying its “plan does not defund or cut existing programs” and it goes on to call the Liberal attack a “pathetic attempt to discredit the NDP.”

“Between 2017 and 2018 the Liberals added $9 billion to program expenses. This included $3.3 billion in program expense growth, which the NDP maintains. And the Liberals added $5.7 billion in new program spending – which the Change for the Better platform replaced with its own new program spending,” says the statement.

The NDP says the Liberal’s latest attack amounts to “fear-mongering.”

The Liberals say economist Mike Moffatt vetted their analysis and called it “accurate.” Moffatt is the director of policy and research at the progressive think tank Canada 2020 and an assistant professor at Western University’s Ivey Business School.

After seeing the NDP’s response, Moffatt said it’s possible the NDP numbers are above board but then wording in the platform is wrong.

Moffatt takes issue with a line in the platform that he says leads to a different interpretation than the NDP intended. The platform says the party’s fiscal framework “shows spending which is in addition to forecasted Liberal government spending, but does not, unless otherwise shown, include new commitments in Budget 2018.”

“There is a mistake in the platform,” Moffatt said in an email. “Either the numbers are wrong, or they mean ‘since Budget 2017’ rather than ‘new commitments in Budget 2018’.”

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