The state of Michigan has told a Canadian energy company it must shut down a controversial oil and gas pipeline by Wednesday amid growing fears that a spill would be catastrophic to the region, in a feud which threatens to strain relations between Canada and the United States.

The company’s refusal to comply with the order, and swift support from top Canadian officials, highlights the politicized nature of pipelines, which campaigners have used as a target in the fight against climate change.

For nearly 67 years, Enbridge has moved oil and natural gas from western Canada through Michigan and the Great Lakes to refineries in the province of Ontario.

But Michigan says that one section to the pipeline – Line 5 – is too risky to continue operating.

In November, the Michigan governor, Gretchen Whitmer, announced a plan to revoke the easement granted to Enbridge, which permits Line 5 to cross under the Straits of Mackinac. Whitmer set 12 May as the deadline for the Canadian energy giant to shut down the pipeline.

“These oil pipelines in the Straits of Mackinac are a ticking timebomb, and their continued presence violates the public trust and poses a grave threat to Michigan’s environment and economy,” Whitmer’s office said in a statement.

The company says it has never experienced a leak in the underwater section of Line 5 and is currently working to tunnel beneath the lake bed to further improve the safety of the pipeline. But in the last two years, the pipeline has been struck by boat anchors and cables. And in 2010, a separate Enbridge pipeline spilled 3.2m litres of oil into Michigan’s Kalamazoo River.

Whitmer, who campaigned on shutting down the pipeline, has received support from Democratic attorneys general as well environmental campaigners and Indigenous communities on both sides of the border.

“Should anything that’s being transported in these 67-year-old pipelines get into the Great Lakes, it would have devastating effects and irreparable consequences,” said the Anishinabek Nation grand council chief, Glen Hare, who represents 39 First Nations across Ontario.

In February, a federal court ordered Michigan and Enbridge to enter mediation. Recently, Michigan has argued that the case should be heard by a state court, which could give it a more favourable judgment.

But international trade lawyer Lawrence Herman says that the United States, not Michigan, is legally bound to keep the pipeline running.

While Line 5 has a smaller range than Colonial, it is just as significant for the region it serves.

Without it, essential products from propane to jet fuel would be cut off or greatly delayed. The alternative plan Whitmer offered for transporting those products - primarily by rail and truck - is ridiculously inadequate.

The surface infrastructure would buckle under such an increased load.

Experts say the Line 5 capacity would most likely be replaced by a larger fleet of tankers.

Those ships would still expose the Great Lakes to the risk of a catastrophic spill.

Even one of Whitmer's predecessors, former governor and now Energy Secretary Jennifer Granholm, declared pipelines as the safest way to carry petroleum.

Whitmer is pursuing a dangerous policy in targeting Line 5 - one that is likely to severely damage Michigan's economy.