The Conservatives are threatening to release more potentially damaging videotapes of Michael Ignatieff in an attempt to discredit the opposition leader.

During Question Period Wednesday, Prime Minister Stephen Harper told the Commons he had lots of tapes featuring Ignatieff.

"I cannot fire the Leader of the Opposition and with all the tapes I have on him, I do not want to," Harper said.

The Conservatives are said to be poring over old video clips of Ignatieff speeches and interviews from his past career as a journalist, author and public intellectual to find potentially embarrassing remarks.

Outside the Commons, Ignatieff described Harper's remarks as "Nixonian", referring to disgraced former U.S. President Richard Nixon who secretly recorded Oval Office conversations, and who was famous of digging up dirt on his political opponents.

"Every day that goes by, he's more like Richard Nixon," Ignatieff said.

"The public finances of our country are in freefall and he's wasting time with tapes of me? It's a joke."

Ignatieff said he won't be intimidated by the prime minister, and that is is his job to hold him to account.

His remarks followed a particularly heated session in the Commons, in which Ignatieff called on the prime minister to fire Finance Minister Jim Flaherty over the ballooning federal deficit.

Harper shot back that the issue at hand should be the "credibility of the leader of the opposition."

Ignatieff is already the subject of several Tory attack ads, which focus on comments he made before entering politics, and the decades he spent outside of Canada.

One ad features an old video interview in which Ignatieff refers to America as 'his country'.

In another Ignatieff is quoted as saying the 'the only thing he missed about Canada was Algonquin Park.'