BC NDP Leader John Horgan says he will travel to Washington to help defend British Columbia's lumber industry in the softwood dispute between Canada and the United States, though he isn't saying whether he'll follow through on a provincial Liberal threat to penalize thermal-coal exports from B.C. ports.

But Mr. Horgan's partner in toppling Premier Christy Clark, Green Party Leader Andrew Weaver, backed Ms. Clark's push for a carbon levy on those coal exports. During the election campaign, Ms. Clark announced her opposition to thermal-coal exports in retaliation to the Trump administration's decision to impose punitive tariffs on Canadian lumber shipments into the United States.

Mr. Weaver, however, isn't sure whether Ms. Clark would have had the power to act on the file. "If it's legally allowable, I am all for it," Mr. Weaver said Thursday, adding that he would also support Mr. Horgan if the NDP Leader pursued action against thermal coal.

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Read more: Canada 'standing up to U.S.' with $867-million for softwood industry, Liberals say

Ms. Clark said during the campaign that she wants to slap a hefty $70-a-tonne carbon levy on exports of thermal coal from B.C. ports, a move that would devastate coal producers in both the United States and Alberta.

Mr. Weaver said it's clear there are greenhouse-gas emissions associated with thermal coal, and Washington State and Oregon have said no to transporting thermal coal through their ports, citing climate change.

Thermal coal – a commodity used in coal-fired electricity plants – is exported through the Westshore terminal south of Vancouver and the Ridley facility in northwestern British Columbia. "B.C. has been a bit reckless in that regard in terms of 'just bring it on.' [But] B.C. could put a price on it," Mr. Weaver said. "It's a bit punitive, but it's fair enough."

Mr. Horgan said on Thursday that he will fulfill a campaign promise that if he becomes premier, he would visit Washington as part of B.C.'s fight against U.S. tariffs imposed on Canadian lumber shipments south of the border.

"I want to help. I want to be available at any time to work with the Prime Minister – to work with other provinces – to make sure that B.C.'s interests are well-represented in Washington and that we're working hard to protect forestry jobs," he said at a news conference in Vancouver. "When I get the opportunity, should I get the opportunity, I'll be working with the federal government to make it abundantly clear that British Columbia has many cards to play and we want to ensure that the United States understands that."

Mr. Horgan is poised to become British Columbia's next premier if plans by his party and the Greens proceed to oust the Liberal minority government.

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The NDP formed an alliance with the Greens to co-operate in the legislature, starting with plans to vote down the Liberals once Ms. Clark reconvenes the legislature. Under a pact announced this week, the three Green members of the legislative assembly elected in the May 9 provincial election agreed to work with the 41 NDP MLAs, combining to outnumber the Liberals' 43 seats.

The two left-of-centre parties plan to bring down the Liberals in a confidence motion that Ms. Clark has said she expects her party will lose, ending 16 years of Liberal government.

Mr. Weaver, whose party holds the balance of power in the minority legislature, said he approves of Ottawa's announcement on Thursday of an $867-million aid package for Canada's softwood industry.

"It's nice that the federal government has stepped up to help out in these uncertain times," he said in an interview in Vancouver after a speech at a clean-energy gathering.

Susan Yurkovich, president of the BC Lumber Trade Council, also welcomed Ottawa's assistance. "This package is a prudent response that can provide both immediate support for workers and communities if required," Ms. Yurkovich said in a statement. "We particularly appreciate the investment in expanding markets for Canada's high-quality forest products overseas, which will help to further diversify our markets."

Ms. Clark said painful times could be in store for many forestry workers due to the U.S. punitive tariffs. "Every time these unfair allegations are tested in an impartial court, we have been successful, and we will be again. Unfortunately, this process takes time, and workers and communities may feel the impact," she said in a release issued by the Premier's office.

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Provincial envoys on the softwood file are David Emerson (B.C.), Raymond Chrétien (Quebec), Jim Peterson (Ontario), Gary Doer (Alberta) and David Wilkins (New Brunswick).

Mr. Horgan said he has full confidence in Mr. Emerson's role as B.C.'s special envoy on the softwood issue.

Right now, five Canadian forestry firms must pay preliminary countervailing duties ranging from 3.02 per cent to 24.12 per cent on lumber shipments, while the U.S. Department of Commerce slapped other producers from Canada with a weighted average duty of 19.88 per cent.

U.S. producers say, under their system, the cost of timber rights on private land is more expensive than the Canadian stumpage fees paid by forestry companies to cut trees down on provincially owned property.