VANCOUVER -- Liberal Leader Christy Clark's bid to ban or tax thermal coal received a boost Friday from the federal government during the provincial election campaign, while NDP Leader John Horgan appealed to Green voters to join him to defeat the Liberals.

Clark issued a statement thanking Prime Minister Justin Trudeau for "carefully and seriously" considering her suggestion to ban or tax thermal coal coming from the United States after it put a tariff on Canadian softwood.

"Banning thermal coal exports through B.C. ports stands up for forest workers and helps fight climate change," she said.

The United States announced a tariff of up to 24 per cent on Canadian softwood last week.

Horgan campaigned Friday on southern Vancouver Island, where Green party officials say they have a chance of winning.

He said the New Democrats have much in common with the Greens.

"All of our common interests will be lost if we have four more years of Christy Clark," he told supporters at a campaign stop in Nanaimo.

Horgan said the Greens and NDP support reforms to the electoral system, reducing greenhouse gases and oppose the Kinder Morgan pipeline expansion.

Minutes after Horgan's comments, Green Leader Andrew Weaver arrived outside the venue where Horgan spoke. He said Horgan's appeal smacks of voter suppression.

"I'm trying to inspire voters," said Weaver, who was on his way to campaign events on the Sunshine Coast.

Clark spent the first part of day defending a little-known tax rebate program meant to attract international business to British Columbia that allowed TD Bank to claim a $2.8-million refund.

Her government challenged the company's claim for the refund in court because TD filed its paperwork a day late. The Court of Appeal ruled last month that B.C. must reconsider the bank's request for a time extension to claim the money.

Clark said the International Business Activity Act has created more revenue than it has cost and it's aimed at luring companies to B.C.

"The evidence tells us it's helping create jobs in British Columbia," she said. "The evidence tells us that it's been a good investment. We need to grow those programs ... that are aimed at attracting head offices from around the world to Vancouver."

The program came under scrutiny this week after a story was published by the New York Times saying it created fewer than 300 jobs while giving $140 million in refunds since 2008.

However, the Liberal party said a study by the government found the program created 1,140 jobs between 2004 and 2007.

The NDP said in a statement that residents deserve answers about a program that allows unnamed corporations to receive an unknown amount of taxpayer money with no discernible benefits for B.C.

The program was created in 1988 when Social Credit was in power. Horgan said it was a modest program under former Social Credit and New Democrat governments.

Since then, he said the Liberals have increased funding for the program by 1,000 per cent.

"This is a program that is giving corporate welfare to one of the most profitable banks in the country. We've asked the auditor general to get to the bottom of this."

Clark, who also campaigned on Vancouver Island on Friday, said the program was always aimed at companies that are going to create jobs in B.C.

"I guess the folks in Finance decided that (TD Bank) met that goal," she said.