TORONTO -- Ontario's Liberal government is slamming the federal Conservatives' proposed expansion to voluntary pension contributions as "playing politics" with people's retirement.

The Harper government announced Tuesday -- less than five months before a federal election -- that it was considering giving Canadians the option to boost their Canada Pension Plan contributions, saying people need choices when it comes to their retirement savings.

But in Ontario, where Premier Kathleen Wynne has long pushed Ottawa to expand the CPP, the provincial government was unimpressed with the voluntary nature of the federal Conservatives' proposal.

"Canadians already have access to a suite of voluntary savings tools, including RRSPs and TFSAs. These tools, however, aren't being utilized," Kelsey Ingram, a spokeswoman for Finance Minister Charles Sousa, said in a statement.

Last year saw Canadians leave $735 billion of RRSP room and $440 billion in TFSA room, she said.

"While the federal government is busy playing politics with people's retirement, our government is taking action."

The jab is the latest in a series of public sparring between Wynne and Prime Minister Stephen Harper over pensions.

Ontario passed legislation last month to create its own provincial plan for more than three million people who do not have a workplace pension, despite critics' warnings it amounts to a job-killing payroll tax. Harper has panned the Ontario plan, saying people prefer tax breaks as a reward for saving for retirement, rather than having their taxes hiked to force them to save.

Wynne has complained that Harper's aversion toward pension reform is "offensive and inexplicable."

When the leaders met in January -- their first face-to-face meeting in more than a year -- it was clear they were so far apart on pension reform that it was not even on the table.

Federal Finance Minister Joe Oliver sent his provincial counterparts a brief letter Tuesday, informing them that he would initiate "informal discussions with stakeholders and industry experts" on a possible "voluntary supplement" to the CPP.

"Although we will not support a mandatory increase to payroll deductions for businesses and workers, we are open to exploring additional measures that provide Canadians with choice," Oliver wrote.

The letter "fails to recognize the role of the provinces as stewards of the CPP," Ingram wrote, noting provinces are not mentioned as one of the groups that will be consulted.

However, Oliver said Thursday that provinces would be included in the consultation process.

The federal Liberals and NDP also characterized the Tories' move as political opportunism on the eve of an election.