For Michigan’s governor, the 645-mile pipeline jeopardizes the Great Lakes. For Canada’s natural resources minister, its continued operation is “nonnegotiable.” The clash over Calgary-based Enbridge’s Line 5, which carries up to 540,000 barrels of crude oil and natural gas liquids across Michigan and under the Great Lakes each day, is placing stress on U.S.-Canada ties — and raising questions about how the close allies, which have expressed a desire to work together to fight climate change, can balance energy security with the transition to a clean-energy economy.

In a move applauded by environmentalists and Indigenous groups on both sides of the border, Michigan Gov. Gretchen Whitmer (D) in November ordered the firm to shut down the nearly 70-year-old lines by May 12. Canadian officials, including Prime Minister Justin Trudeau, have appealed to their American counterparts, including President Biden, Secretary of State Antony Blinken and Energy Secretary Jennifer Granholm for help.

Joe Comartin, Canada’s consul general in Detroit, said a shutdown would have “significant” impacts on both sides of the border. He predicted effects ranging from months-long propane shortages to higher costs for consumers to fuels being carried by rail, truck or boat — methods that he said are less emissions-friendly and more dangerous than a pipeline.