Prime Minister Stephen Harper and several of his Conservative MPs pounced on Liberal leader Justin Trudeau’s position on the Canada Pension Plan during question period on Thursday.

After the Conservatives announced Wednesday their willingness to consider voluntary expansion of the CPP -- an idea the party had long dismissed – Trudeau said he supports a “mandatory” expansion of the CPP “of the type Kathleen Wynne put forward in Ontario.”

Premier Wynne was re-elected in 2014 after promising an Ontario pension plan where employers and employees will each contribute a percentage of earnings. According to the Ontario Liberals, the average worker who earns $45,000 will pay $788 into the plan in exchange for about $6,400 per year in old age. That would be on top of the $6,800 average benefit that retired Canadians currently get from the mandatory Canada Pension Plan.

The Prime Minister referenced Trudeau’s pension position Thursday in response to a question from Liberal MP Scott Brison, who said the Conservatives had added $150 billion to the debt, while the Liberal governments preceding them had paid down debt.

“Here’s something else he can try to defend,” the Prime Minister responded. “The Liberal leader saying yesterday he favours a mandatory expansion of the CPP of the type Kathleen Wynne put forward. That’s a $1,000 pay cut for every single Ontario worker earning $60,000 a year, just from their own pockets.”

The Prime Minister later called the mandatory CPP increase is “a tax,” adding, “Canadians want more money in their pockets, not less.”

Conservative MPs Susan Truppe, Jeff Watson, Robert Sopuck, Kevin Sorenson also all quoted Trudeau and slammed the idea of mandatory CPP expansion.

The NDP and the Green Party also support a mandatory increase.

Green Party Leader Elizabeth May defended her position on CTV Power Play by saying that CPP “is reliable, sustainable and has proven its value.”

NDP MP Robert Chisholm said that mandatory expansion of CPP “makes good economic sense,” and that the government should also turn back the retirement age from 67 to 65.

“Not dealing with the retirement income right now and not rolling back the Old Age Security eligibility to 65,” he added, “is going to mean we’re having increasing levels of poverty for seniors.”

Liberal MP John McCallum, meanwhile, told CTV Power Play that mandatory increase to CPP is “an idea whose time has come.”

He added, “it is essential for Canada -- if we want our seniors to have a decent retirement living -- to take the bull by the horn, work with the provinces and expand the CPP.”