The environmental fight over Enbridge Inc.’s dual-pipe oil Line 5 across Michigan escalated Monday into the first-ever use of a 44-year-old energy traffic treaty between Canada and the United States.

Enbridge Line 5

Canadian Foreign Affairs Minister Marc Garneau announced that a formal request has been made to save the 540,000 b/d conduit with a dispute resolution and arbitration process in a 1977 Transit Pipelines Agreement between the two countries.

The treaty “prohibits measures that are intended to impede, divert, redirect or interfere with crude oils or natural gas liquids moving through transit pipelines, such as Line 5, or that would have that effect,” said Garneau.

“Today Canada is formally invoking the dispute settlement provision of the 1977 Agreement to ensure its full...