Enbridge Inc. served notice Tuesday that Canadian oil would continue to flow across the Straits of Mackinac regardless of an order by Michigan’s executive branch to shut down the 540,000 b/d Line 5 in mid-May.

Gov. Gretchen Whitmer and Attorney General Dana Nessel have no power to enforce their notice issued in November that the pipeline be evicted as of May by erasing the Straits easement that enabled its construction 67 years ago, said the Calgary-based firm.

“The state lacks the authority to terminate or revoke the 1953 easement,” stated a letter from Enbridge Vice President Vern Yu to Whitmer and Daniel Eichinger, executive division director of the Michigan Department of Natural Resources.

Enbridge in November vowed “a thorough response through the legal...