This 2002 photo shows the Mackinac Bridge that spans the Straits of Mackinac from Mackinaw City. Gov. Gretchen Whitmer ordered Canadian energy company Enbridge last fall to shut down Line 5 — a key piece of a crude delivery network from Alberta’s oil fields to refineries in the midwestern U.S. and eastern Canada. A section roughly four miles long crosses the bottom of the Straits of Mackinac, which connects lakes Michigan and Huron. (AP photo)

TRAVERSE CITY — Months after President Joe Biden snubbed Canadian officials by canceling Keystone XL, an impending showdown over a second crude oil pipeline threatens to further strain ties between the two neighbors that were frayed during the Trump administration.

Michigan Gov. Gretchen Whitmer, a top Biden ally, ordered Canadian energy company Enbridge last fall to shut down Line 5 — a key piece of a crude oil delivery network from Alberta’s oil fields to refineries in the midwestern U.S. and eastern Canada.

Whitmer’s demand pleased environmentalists and tribes who have long considered the pipeline, which reaches 645 miles across northern Wisconsin and Michigan, ripe for a spill that could devastate two Great Lakes.

A section roughly four miles long crosses the bottom of Michigan’s Straits of Mackinac, which connects Lake Michigan and Lake Huron. The area is a popular tourist destination, and several tribes have treaty-protected commercial fishing rights in the straits.

But with the governor’s May 12 shutdown deadline approaching, Canadian officials are lining up behind Enbridge as it contests the order in U.S. court and says it won’t comply. The Calgary-based company says Whitmer is overstepping her authority and that the 68-year-old pipeline is sound.

“Our government supports the continued safe operation of Enbridge’s Line 5,” Seamus O’Regan, Canada’s minister of natural resources, told The Associated Press in an email. “It is a vital part of Canadian energy security, and I have been very clear that its continued operation is non-negotiable.”

A Canadian House of Commons committee this month warned of dire consequences from a shutdown: job losses, fuel shortages and traffic nightmares as 23 million gallons of petroleum liquids transported daily through Line 5 are shifted to trucks and rail cars considered more susceptible to accidents.

The panel urged Prime Minister Justin Trudeau and other Canadian officials to lobby their U.S. counterparts and said that without an agreement, Canada might invoke a 1977 treaty barring either nation from hampering oil and natural gas transmission. O’Regan’s office said the matter had been raised at the “highest levels” of federal and state governments.

The dispute comes as both nations hope to reset their relationship after the presidency of Donald Trump, who put tariffs on Canadian steel and aluminum and had a turbulent relationship with Trudeau. Biden’s first meeting with a foreign leader was a virtual session with Trudeau in February, where they pledged cooperation on climate change and other matters.

Biden’s cancellation of Keystone XL, a 1,200-mile pipeline from Alberta’s oil sands, remains a sore point in Canada. Although Trudeau objected to the move, Alberta officials are “extremely disappointed” he isn’t taking stronger action, said Sonya Savage, energy minister in the province home to most of Canada’s oil production.

Now comes Line 5, which few Americans outside the Great Lakes region may know about. But it’s a priority for Canada, the world’s fourth-largest producer and third-largest exporter of oil.

“The Canadians are likely to make this their big issue,” said Christopher Sands, director of the Canada Institute at the Wilson Center, a global policy think tank in Washington, D.C. “This is one where I don’t think (Trudeau) can afford to back down.”

While the Keystone project was halted in early construction, Line 5 has transported Canadian oil since 1953. More than half of Ontario’s supply passes through it, according to Enbridge. It exits Michigan at the border city of Sarnia, Ontario, and connects with another line that provides two-thirds of the crude used in Quebec for gasoline, home heating oil and other products.