Prime Minister Stephen Harper continued to defend the Senate Wednesday as opposition MPs took aim at the number who wouldn't answer CBC News questions about where they really live.

After weeks of questions about living expenses and whether some senators live in the right province and qualify for their seats, CBC News found 25 of 104 senators either refused to say they had proof of their primary residence or wouldn't respond to questions. Most of them — 21 — were named to the Senate by Harper, who came to power in 2006 promising accountability and Senate reform.

NDP Leader Tom Mulcair pushed the prime minister on the issue in question period.

"In their eighth year of broken promises, this is the Conservative record on Senate reform," Mulcair said. "Will the prime minister decide that his senators, members of his caucus, come clean with Canadians, or is he going to keep covering up for them?"

Harper blamed the New Democrats for not supporting his efforts at small reforms to the Senate. The NDP want to see the Senate abolished entirely.

"All senators conform to residency requirements. That is the basis on which they are appointed to the Senate and those requirements have been clear for 150 years," Harper said.

"Unfortunately it is the NDP that consistently opposes reforming the Senate and opposes an elected Senate."

Since CBC News reported the list of senators on Tuesday, three more have answered questions about their residency and what supporting documents they have to prove it.

That leaves 22 who haven't answered or haven't listed the supporting documents they have, of whom 18 were chosen by Harper.