OTTAWA - Tom Mulcair was labelled an anti-trade, anti-business extremist Wednesday for threatening to rip up a controversial investment treaty with China.

But the NDP leader did not back down. Indeed, he ratcheted up the rhetoric against the Foreign Investment Promotion and Protection Act, vowing that an NDP government would not be bound to honour a treaty ratified by the Harper government.

"Let me be very clear," Mulcair told the House of Commons.

"The Conservatives will not tie the hands of the NDP. We will revoke this agreement if it is not in the best interests of Canadians."

Prime Minister Stephen Harper said the treaty is the product of almost 20 years of negotiations, designed to give Canadian investors in China the same protection that Chinese investors have in Canada. He ridiculed Mulcair's threat to abrogate the deal.

"The leader of the NDP is saying he would revoke the hard-earned right of Canadian investors to be protected in a marketplace like China. That is precisely why Canadian investors, the Canadian business community and the Canadian public at large does not trust the NDP with economic policy," Harper said.

"New Democrats support trade," retorted Mulcair. "We just do not support selling out Canada."

Harper countered that the NDP has opposed almost every trade deal Canada has ever struck with any country, including calling the free trade agreement with the United States a "sellout."

"That kind of extremism on trade is why Canadians will never entrust economic policy to the NDP," he declared.

The sparks have been flying over the investment agreement for several days as opposition parties, bolstered by a grassroots letter-writing and petition campaign by activists, push for fuller debate on the deal, which is to be ratified within days.

Interim Liberal leader Bob Rae joined Mulcair on Wednesday in demanding more details about the treaty and more time for Parliament to examine it.

Rae maintained the agreement does not guarantee Canadian investors greater access to the Chinese market. He questioned the secrecy surrounding the deal and why it includes a provision requiring 15 years notice for either country to withdraw from it, when most other trade and investment deals contain notice periods of a year or less.

The government's lack of transparency "creates suspicion in the public that there's something to hide," he said.

Nevertheless, Rae too piled on Mulcair for threatening to abrogate the treaty, noting that the NDP has opposed every investment and trade treaty "that's ever been signed by Canada." By contrast, he said Liberals favour more open trade, provided it is reciprocal and fair.

Mulcair said the NDP "has tried every technique" at its disposal to get more transparency and more debate on the treaty, without success. While the Harper government has every right to ratify the deal, he said an NDP government would be equally entitled to review it and, if necessary, withdraw from it.

Critics say the deal would give state-owned Chinese corporations new powers to influence Canadian policy on everything from investment and industrial development to environment, health and natural resources. They also say it could negatively impact on the jurisdictions of provinces, which weren't consulted.

Joan Bryden reports for the Canadian Press.

*This story's headline was changed at 5:27 p.m.