The NDP and Conservatives let fly duelling fact-check memos Monday as they clashed over what makes a carbon tax, who wants to change the Senate and which party is telling the truth.

Conservative MPs maintain that NDP Leader Tom Mulcair wants to introduce a carbon tax in Canada. Both the Conservatives and the NDP proposed a cap-and-trade system during the 2008 campaign — an idea the Tories have since abandoned.

Despite the cap-and-trade promise being clearly stated in their platform, the Conservatives have continued to insist the NDP plan would have been a tax and that it reflects badly on Mulcair and his party.

'A "price on carbon" is a tax on carbon. That makes it a carbon tax.'—Conservative Party spokesman Fred Delorey

Conservative Party spokesman Fred Delorey issued a "fact check" to reporters Monday morning, quoting NDP House Leader Nathan Cullen saying he's "more of a cap-and-trade kind of guy," but that it's important to put a price on carbon.

"A 'price on carbon' is a tax on carbon. That makes it a carbon tax," Delorey's statement says.

The NDP fired back with a statement mimicking the style of the Conservatives' internal talking points memos.

"The Conservatives have a secret plan to impose a carbon tax," the NDP statement says, before quoting the Conservative Party's 2008 platform.

Conservatives promised cap and trade in 2008

"We will work with the provinces and territories and our NAFTA trading partners in the United States and Mexico, at both the national and state levels, to develop and implement a North America-wide cap and trade system for greenhouse gases and air pollution, with implementation to occur between 2012 and 2015," the Conservative Party's platform said.

The NDP also quote Environment Minister Peter Kent, who said last year that a cap-and-trade system is a possibility for Canada.

"According to the Conservatives own twisted logic, Conservatives planned to impose a carbon tax between 2012 and 2015, and are still actively considering a carbon tax in the future. The well documented reality is, the NDP has opposed a carbon tax in the past and continues to do so now," the NDP release says.

Government House Leader Peter Van Loan raised the carbon tax allegation Monday morning in a scrum with reporters. He also made a bizarre attack on the NDP over the government's Senate reform legislation, given that the NDP have for years called for the Senate to be abolished.

'The Conservatives are entitled to their opinions but not their own facts.'—NDP House Leader Nathan Cullen

"[Bills to reform the Senate] have been consistently resisted, not surprisingly by the Liberals — I understand they don't want any changes to the Senate — but more surprisingly, by the NDP, who have been pulling out every stop to defend the status quo," Van Loan said, adding that the government doesn't want to ram a bill like that through Parliament.

"If the NDP were prepared to support [the bill], if the opposition parties were prepared to support it, I'd call it today and we'd have it passed through the House of Commons this week."

Cullen, in his own scrum with reporters, called for a debate on substantive issues rather than mud-throwing.

"The Conservatives are entitled to their opinions but not their own facts. They can repeat lies and hope that one day that somehow becomes the truth in the minds of Canadians, but it's not the fact. I wish we could actually deal with the substantive matters. This government has no climate change policy whatsoever, has been promising one for years and has continued to break that promise, session after session."

Senate reform debate

Cullen said Prime Minister Stephen Harper has shown hypocrisy in appointing more than 30 "new friends" to the Senate, despite the desire he's expressed in reforming Parliament's upper chamber.

"If there's a chance to work on the Senate, we're open, but the details are incredibly important to us," Cullen said.

Van Loan confirmed the government will be using another omnibus bill to implement the next phase of the federal budget. Critics charged last spring that a bill with more than 400 pages made it hard to debate the government's measures in the House and examine them in committee.

Van Loan says it's standard to use massive bills to bring in the legislation that supports the budget. However, until the Conservatives took government in 2006, the longest budget implementation bill to receive Royal Assent was 144 pages. Since 2006, the size of the Conservatives budget implementation bills has varied from 60 pages at Royal Assent to 904 pages.