Cries of lies and tax hikes were hurled across the House of Commons as the Liberals and Conservatives clashed over a policy that hasn't even been announced yet.

"When are the Conservatives going to stop insulting Canadians and offer a real plan to tackle climate change instead of cartoons and a campaign of lies," asked Liberal Leader Stephane Dion on Monday.

He was referring to a new Tory ad campaign about the Liberals' looming carbon tax proposal -- a policy that has yet to be released.

Jason Kenney, secretary of state for multiculturalism and the Canadian identity, retorted that the Liberal plan would be a massive tax grab.

"Even while gas prices are going up, he wants to force them higher, with higher taxes to pay for the billions of dollars of unbudgeted promises," he said as some Tory MPs held up postcards from the campaign talking about Dion's "tax on everything."

Some reports have indicated the tax won't apply to gasoline.

Speaker Peter Milliken rebuked Dion for using the word "lie" in his questions.

Deputy Liberal Leader Michael Ignatieff said in the government's regulations for greenhouse gases, it admits that higher energy costs will result for consumers.

"Nowhere does the Conservative plan propose to help seniors and low-income Canadians bear those costs. Our plan will," he said.

"When will the 'little grease spot' (from the ad) start telling the truth?" Ignatieff asked.

Kenney noted Ignatieff, unlike Dion, had previously supported a carbon tax.

The Liberal caucus is already showing some public divisions over the timing of the carbon tax plan.

In a blog posting, Liberal MP Garth Turner slams the Tories for their "pathetic and disappointing" ads but he says the tax is "too crucial to bring forth at the wrong time."

Turner said there are two possible moves for the Liberals in response to the ads.

"The damn-the-torpedoes response would be to push ahead simply because this is the right thing to do for our wasteful, oil-drunk society and collective future," said Turner.

"The political reaction would be to modify and corrupt the plan to address worries of rising energy costs and pissed-off voter groups. Since Stephane Dion is one of the most principled people I have encountered in public life, and yet a national party leader who needs support, I don't know the outcome."

But he said the "avalanche" of emails and blog comments he's received were telling.

"Either this is not the time for altruism, with $140-a-barrel oil, or proponents of the Green Shift have simply not articulated their vision," said Turner.

'Political games'

Ottawa Liberal MP David McGuinty, the opposition's environment critic, said he "hopes the ads run every 15 minutes" so Canadians are reminded of what he sees as the Conservative government's shady political tactics.

"If the Conservatives want to race to the bottom they are OK to do so," he told CTV Newsnet on Monday. "Last week in Canada we lost about 2,000 high-paying jobs (at General Motors) and this is what the prime minister is doing with his time and energy.

"They're playing political games with the future of our climate and our atmosphere and it's not surprising at all."

In the plan, tax would be levied on polluting items but income tax would be reduced, said McGuinty. That means Canadians choosing to drive less would have more money to spend otherwise.

Green Party Leader Elizabeth May supports the idea and thinks a carbon tax is one of the few ways to encourage Canadians to get used to oil's ever-increasing price tag.

"It is bold. It does take leadership," she said. "The reason the prices at the pump are going up is because we're at the end of cheap fossil fuels... I think that there's never a bad time to tell Canadians the truth."

CTV's Ottawa Bureau Chief Robert Fife said the Tories are introducing the ads now because gas prices are so high and people are heading into their summer vacation.

"We know that the (Liberal) caucus is really divided about it (the carbon tax) but nobody has really publicly come out and talked about it but now we're starting to see that these Tory attack ads are having their effect," Fife said Monday.

The ads will run in Toronto and other parts of southern Ontario, and will be accompanied by standard radio ads, t-shirts, postcards and other materials.

The ads feature what appears to be a talking smudge of oil on a gas pump, with a van in the background.

One of the 15-second spots says:

"(Liberal Leader) Stephane Dion said he wasn't going to introduce a carbon tax. But now he is. Yet another flip-flop."

There are three such "fuelcast" ads at the website willyoubetricked.ca.

However, Fuelcast, the company that operates the ad system, said Monday it won't run the Conservative ads at the pumps because it has a policy against political advertising.