BC Liberal Leader Christy Clark says her threat of a ban or a tax on thermal coal exports, announced just over a week before a provincial election as a shot at the United States over the softwood lumber dispute, would proceed regardless of whether Canada and the United States reach an agreement to end the trade battle.

Ms. Clark announced her desire to target thermal coal exports, the majority of which comes from the United States, as part of the province's response to the U.S. decision to impose tariffs on Canadian softwood lumber.

She first asked Ottawa to ban exports but then said a re-elected BC Liberal government would impose a tax on thermal coal from B.C. ports if the federal government did not act.

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British Columbia is Canada's largest lumber exporter to the United States.

Ms. Clark, in a roundtable meeting with The Globe and Mail's B.C. bureau on Wednesday, described targeting thermal coal as the "right thing to do" – a measure she had long been intent on pursuing and had discussed with Jay Inslee, the Governor of Washington State, who she said shared her concerns. However, Ms. Clark said Washington and other states lacked the power to impose their own bans on thermal coal.

She said she held off taking action to avoid disrupting talks on a new softwood-lumber agreement.

"When the Americans slapped a 20-per-cent duty on our softwood lumber, that freed my hand to make sure we were going to do something I thought was the right thing to do," said Ms. Clark. "The coal is the dirtiest electricity-producing product out there."

The measures would also apply to coal imported into B.C. from neighbouring Alberta.

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At the same time, Opposition New Democrat Leader John Horgan, whose party is polling strongly ahead of next week's election, said an NDP government would not be bound by Ms. Clark's sabre rattling, but he did not say whether he would pursue the same measures.

On another front in the softwood dispute, Ms. Clark said she has worked out an aid package with the federal government to assist forestry workers and companies that are hurt by the softwood impasse.

"We will be ready with a package for loans to support companies that are in distress, if that's what they need," she said, "and to support workers with enhanced EI benefits, if that's what they need."

She said government will also support legal fees for industry until an agreement is reached.

Publicly released opinion polls have suggested next week's election could be extremely close. The Liberals are seeking a fifth consecutive governing mandate. Ms. Clark succeeded Gordon Campbell as party leader in 2011 and was elected in her own right in 2013. The NDP is seeking a return to power after 16 years in opposition.

Banning thermal coal hinges on federal approval. Last week, Ms. Clark wrote a letter to Prime Minister Justin Trudeau asking him to impose a ban on thermal-coal exports from B.C. ports. The coal goes into coal-fired ports to generate electricity.

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Ms. Clark said the ban on thermal coal would create space in B.C. terminals for cleaner forms of coal. Since proposing the ban, Ms. Clark has also threatened to impose a $70-a-tonne carbon levy on exports of thermal coal from British Columbia ports. The proposed levy would render the $100-a-tonne export uneconomic, inflicting deep losses on producers intent on shipping overseas.

She said B.C. is considering other retaliatory measures on the softwood file regardless of the outcome of the federal decision. "We have a backup plan and we're going to bring that into force if we don't get a yes," she said.

"You'll see if we need to use them."

The prospect of the B.C. levy has raised concerns in Alberta given the possible economic impact there as thermal coal is shipped from that province. Ms. Clark said she has not spoken to Alberta Premier Rachel Notley about the issue.

Mr. Horgan, who also met with The Globe's B.C. bureau on Wednesday, said an NDP government would not be bound by Ms. Clark's positions on thermal coal.

"What would I do as the leader of the government of British Columbia? I'd use all the interests I have at my disposal, working with the federal government," Mr. Horgan said when asked whether he would stick with the retaliatory levy on carbon proposed by Ms. Clark.

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"I am not bound to anything the BC Liberals have done. I am seeking to form a new government," said Mr. Horgan, adding he would talk to provincial ministry officials to come up with the "best plan" to protect B.C. jobs.

Mr. Horgan has said he would also reach out to Ottawa on the file, and promised a trip to Washington to make the case for British Columbia's interests on getting a deal.

Pressed, however, on whom he would meet, the NDP Leader said he had not laid out an itinerary for such a visit at this point. "Our best outcome is a negotiated settlement. We need to fix this. We have known that since the last deal was struck."

With a report from Justine Hunter