The leaders of Canada's federal political parties traded accusations over soaring gas prices and consumer costs while pumping their respective proposals to voters on the federal election campaign trail Friday.

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NDP Leader Jack Layton, right, shares a laugh with NDP candidate Jack Harris, Ed White, his wife Joan White and their granddaughter Drew MacKillop during a campaign stop in St. John's on Friday. ((Andrew Vaughan/Canadian Press))

The appearances came after motorists in many cities were surprised to discover the price of gasoline had risen by as much as 13 cents a litre overnight, even as oil prices dipped beneath $100 for the first time in five months.

NDP Leader Jack Layton pledged to attack the "predatory pricing" that he said is contributing to the income squeeze of Canadian families, saying his party would hold banks and gas companies accountable for their pricing.

Saying big oil "shouldn't have a free licence to gouge consumers," Layton pledged to bolster the Competition Bureau in its investigation of alleged price-fixing and appoint a gas prices ombudsman as part of his consumer protection plan.

Layton added that some of his proposals are already in practice in several other countries, including the United States, Britain and France.

"These are measures which governments that actually stand up for working families put into place," Layton said at a campaign event at a family home in St. John's. "It's really surprising to a lot of Canadians that our governments seem to refuse."

Green Shift won't tax at pumps: Dion

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Conservative Leader Stephen Harper answers reporter's questions at a campaign event in Halifax on Friday. ((Tom Hanson/Canadian Press))

Campaigning Friday in British Columbia, Dion defended the Liberals' Green Shift plan as a combination of $15 billion in tax cuts with increases in energy costs, though not at the gas pumps, saying it was "good for the environment, good for the economy."

"We don't tax at the pump," Dion said at a campaign appearance at a green housing co-operative in Burnaby, while adding the plan would provide middle- and low-income families with up $2,400 each a year through the tax cuts.

The Liberal leader accused Harper of "fear-mongering" in his attacks of the plan, saying his claim that the Green Shift would plunge Canada into a recession has been ridiculed by economists.

"Mr. Harper is not speaking the truth; he is fabricating," Dion said.

He also ridiculed Harper's campaign pledge to cut two cents off the excise tax on diesel fuel, calling it a "gimmick."

"Yesterday, the cost of diesel went up by two cents," Dion said.

Dion said his Green Shift plan calls for the strengthening of the Competition Bureau by giving it powers to investigate suspected price-gougers through civil as well as criminal law.

But the main reason why the price of oil is set to go up even more, Dion said, is because "humanity is asking for more and more."

"The countries that give to themselves the possibilities of being more energy-efficient and to develop renewable resources of energy are the winning countries of the 21st century," Dion said. "And the world will buy their solutions."

High price of gas 'appears' to be gouging: Harper

When asked during a campaign stop in Nova Scotia whether Friday's gas prices suggested price gouging, Conservative Leader Stephen Harper replied: "Well, it certainly appears that way to me." 

But Harper did not promise any immediate action to lower gas costs.

"I've learned not to make policy on a day-to-day basis," Harper told reporters after a speech to the Halifax Chamber of Commerce, where he outlined his party's plan to relax foreign investment rules.

Harper said his government is continuing to help Canadians contend with higher prices, citing the reduction of the GST to five per cent and the diesel excise tax plan.

He also kept up his criticism of his opponents' environmental proposals, saying Dion's Green Shift carbon tax would lead to even higher gas prices and is "a policy that is so out of touch here, it's almost off the radar."

The Conservative leader also warned the NDP's environmental plan could bring just as much harm to the Atlantic region.

He said Layton has talked of shutting down development of the oilsands, "which people forget employs a lot of Atlantic Canadians and brings a lot of money to this region of the country.

"I understand they want to attack the government for certain things where they think it's popular or whatever," Harper said of his opponents. "But their policies are not thought through as serious governing options for the country, and they will have very serious effects in regions like Nova Scotia."

Dion may face a tough sell to voters in B.C. who are already contending with a provincial carbon tax that kicked in on July 1 and added 2.3 cents to the price of a litre of gasoline, said the CBC's Julie Van Dusen, who is covering the campaign from Ottawa.

The increase is "not going over well," Van Dusen said, and is giving a boost to the provincial NDP, which has been lambasting the tax despite its initial popularity.

B.C. features a number of tight contests in key ridings between the Conservatives, the NDP and the Liberals.  

Also on Friday, Green party Leader Elizabeth May was in Toronto announcing her party's green-business policy platform.

Tories looking for campaign boost in Atlantic

The Harper campaign sought to improve its fortunes a day after the campaign suspended its communications director for questioning the political motives behind the comments made by the father of a fallen Canadian soldier, Van Dusen said.

Harper spent Friday afternoon in the western P.E.I. riding of Egmont before an evening rally in Summerside. Egmont is considered the Tories' best chance for winning a seat on the Island, which has four ridings. P.E.I. has elected only Liberals to Ottawa since 1984, but Egmont incumbent Joe McGuire is not reoffering.

The Conservatives have a strong candidate in Gail Shea, a former provincial cabinet minister, but she has a difficult task in unseating the Liberals. Their candidate, Keith Milligan, is a former premier, and McGuire won the seat in 2006 by more than 4,000 votes.

The Conservative leader is expected to make his first formal appearance in Newfoundland and Labrador on Saturday.

Harper was the subject of a blistering speech on Wednesday by Progressive Conservative Premier Danny Williams, who described Harper as a "fraud" hoping to implement a far-right agenda on Canadians if he forms a majority government.

Layton sees the province as fertile ground to pick up a couple of seats vacated by veteran Conservatives Loyola Hearn and Norm Doyle, Van Dusen said.