ST. IGNACE, Mich. (Great Lakes News) – Canada has invoked a 1977 treaty in a dispute with the U.S. to stop Michigan from closing Enbridge Energy’s Line 5 pipeline in the Straits of Mackinac.

A Canadian government attorney notified a federal judge in Grand Rapids of the invocation of the treaty.

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Line 5 is a major energy source for Canadians as well Michigan residents, particularly those in the Upper Peninsula.

Gov. Gretchen Whitmer says she is “profoundly disappointed” in the actions from Canada, saying as long as oil is flowing, there is a “very real threat of a catastrophic spill in the Great Lakes.”

Gov. Whitmer threatened to shut down Line 5 in May with no plan in place of how energy would be distributed to Michigan’s residents.

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Canadian-based Enbridge ignored Whitmer’s deadline and the sides are embroiled in a legal battle.

The company had an agreement under former Michigan Gov. Rick Snyder to move the pipeline to a tunnel under the Straits.

Enbridge has operated the pipeline for 60 years with no spills. It’s spending $500 million of its own money to build a tunnel that would encase Line 5.