MONTREAL, Sept. 11 (UPI) -- A carbon tax plan by Canada's Liberal Party will plunge the nation into recession, Conservative Prime Minister Stephen Harper said Thursday.

It will also spark economic unrest that will revive Quebec's separatist movement, Harper said in a campaign speech.

"By undermining the economy and re-centralizing money and power in Ottawa, it can only undermine the progress that we have been making on national unity," Harper told a Montreal breakfast audience.

Liberal leader Stephane Dion responded, saying Harper's assertion was irresponsible and used the lowest kind of politics, The Toronto Star reported.

"I do not need any lessons from Stephen Harper on fighting for the national unity of my country," Dion told a business group in St. John, New Brunswick.

"We must stop elevating every policy difference into a national unity crisis," he said. "It is completely irresponsible for Stephen Harper to do this."

He called the Liberals' proposed ecotax a "courageous plan for all of Canada" and said debating its merits "doesn't threaten the future of our country, it makes us stronger."

The Liberal plan proposes new taxes on fossil fuels, in a bid to curb their use, coupled with income-tax cuts to offset the ecotax's effects.

Harper acknowledged this week that the Conservatives' greenhouse-gas strategy would not be "costless," but did not address its effects on consumers, the Star said.

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