– While much of the world may be focused on President Donald Trump’s threats of a trade war with China, Canada’s attention right now is on a commercial feud within its own borders.

The provinces of British Columbia and Alberta are locked in a battle over a $7.4 billion expansion of a pipeline that runs from Alberta’s oil sands to a tanker port near Vancouver, a plan approved long ago.

Many British Columbians fear that increased tanker traffic could lead to spills along a coastline that is a global tourist attraction. Alberta argues that the pipeline is vital to its energy industry and the entire Canadian economy.

The rhetoric and threats from both provinces has often been intemperate, and the dispute has put Prime Minister Justin Trudeau in a difficult situation, forced to choose sides in an argument that boils down to the economy on one hand and the environment on the other.

In a potentially risky political move for a leader who has put fighting climate change high on his agenda, Trudeau has declared the pipeline to be in the national interest and vowed that it will be built.

The dispute has been festering for months. But the tension peaked when the pipeline’s owner, Kinder Morgan of Houston, said recently that it is suspending all nonessential spending on the program.

The company gave British Columbia until the end of May to end its attempts to delay or block the project. If not, the company said it would cancel its plan to add a second pipeline along a route that opened in 1953.

To try to resolve the standoff, Trudeau has summoned Rachel Notley, the premier of Alberta, and John Horgan, her counterpart in British Columbia, to Ottawa for talks on Sunday.

Given the intransigence of both sides, even Trudeau’s top officials are playing down the idea that the conversation will end the battle. But it may provide a glimpse of how Trudeau intends to grapple with an issue in which any resolution will inevitably alienate some voters, and on which there isn’t a clear national consensus.

“Canadians are quite divided,” said Shachi Kurl, the executive director of the Angus Reid Institute, a nonprofit polling firm based in Vancouver. “So much of this debate is rural versus urban Canada.”

Tankers filled by the current Kinder Morgan pipeline now sail to refineries on the West Coast of the United States. The extra capacity from an expansion could, in theory, allow oil sands companies to also begin shipping to Asian markets where demand for oil is growing, said Andrew Leach, an energy and environmental economist at the University of Alberta.

Notley, and her left-of-center New Democratic Party, surprised the Canadian political world in 2015 by bringing four-and-a-half decades of Progressive Conservative rule to an end in Alberta. While she vowed in her campaign to take on the big oil interests in the province, politically she has no choice but to be a booster of the pipeline. Polls show that Albertans overwhelmingly want the expansion to go ahead.

To defend the expansion, the premier has shown a willingness to get tough with her provincial neighbor to the west. Earlier this year, Notley briefly banned imports of wine from British Columbia.

And unless the meeting Sunday changes her mind, Notley’s government is expected to introduce legislation in the coming week that will give it the ability to restrict oil and gas shipments to British Columbia, driving up prices in the province.

This past week, Notley suggested that if Kinder Morgan decides not to go ahead with the expansion, the provincial government might buy and build the pipeline. Officials in Trudeau’s Cabinet have suggested that the federal government might support such a plan.

For Horgan in British Columbia, the political calculus surrounding the pipeline expansion was more complex. The project is widely opposed in the areas around Vancouver and Victoria, the provincial capital, according to Kurl, the pollster. But support is strong for it elsewhere in the province, where resource industries are big employers.

Perhaps tipping the scale in his decision to try to block the project is that Horgan, also a member of the New Democratic Party, relies on the support of three Green Party members to pass legislation. That party, like many environmental groups, argues that Canada should not be building oil pipelines while it is attempting to reduce greenhouse gas emissions.

So Horgan plans to ask a court to determine if British Columbia can use local permits and provincial environmental laws to block the pipeline.

Trudeau’s government has cited several decisions, including some from the Supreme Court of Canada, that it contends give Ottawa complete authority over interprovincial pipelines. But it appears that the federal government can do nothing to stop Horgan from going to court.

Environmental groups and some indigenous groups have vowed to stop the pipeline expansion through widespread civil disobedience.

“In an ideal world, we would like to see the federal government recognizing that it made an egregious mistake in approving this pipeline,” said Cam Fenton, a Canada strategy manager for 350.org, a nonprofit that opposes new fossil fuel projects. “At the end of the day polls change, science doesn’t. And it says we cannot deal with climate change and build pipelines.”