Ontario NDP candidate Charlie Angus is questioning the way the Liberals have costed their $2.6-billion pledge for First Nations education, saying the party has promised to top up a Conservative promise that no longer exists.
Angus, a longtime advocate for First Nations issues, said the Grit costing documents include a $1.7-billion shortfall.
"I'm actually very let down that Justin played this game because I thought it was a strong benchmark," Angus said in a phone interview.
Trudeau defended his party's numbers Tuesday at a campaign stop in Winnipeg.
"We have been very clear on this from the initial announcement up to our costing platform," Trudeau said.
"The federal government, under Stephen Harper, announced funding for First Nations education ... that it had actually never spent. It is money that exists within the current budgetary framework but has not been spent yet on First Nations education."
Trudeau said his party intends to top up the unspent money with "hundreds of millions of dollars more every year" to ensure First Nations education is properly funded.
"That is both money that the federal government promised but hasn't spent a penny of yet and money that we are adding because making sure we move toward parity for First Nations education is a goal that all Canadians can understand."
But Angus said the math still doesn't add up.
"The Conservatives promised that money and pulled it back, so it's not there," Angus said.
"He's counting a broken promise as financial numbers so Conservative broken promise, Liberal broken promise ... we need to actually see the dollars so we can build these schools and get kids the math textbooks and the science labs that they need."
First Nations education has long been a bone of contention between aboriginal groups and the Conservative government.
Perry Bellegarde, national chief of the Assembly of First Nations, has urged the federal government to return to the table in the wake of an education deal that fell apart during Shawn Atleo's time at the helm of the AFN.
In February 2014, Prime Minister Stephen Harper publicly announced the $1.9-billion deal with Atleo in front of the national media.
That arrangement unravelled after some aboriginal leaders complained of a lack of consultation, accusing the Conservatives and Atleo of engaging in "back-door dealings."
The controversy ultimately led to Atleo's resignation.
In their budget released this spring, Conservatives earmarked $200-million a year over five years beginning in 2015-16 for First Nations education.