Canada invokes 1977 treaty with US as dispute over pipeline intensifies

Michigan governor Gretchen Whitmer says Line 5 of pipeline is a ticking time bomb' and has ordered it shut down

The Canadian government has invoked a decades-old treaty with the United States in its latest bid to save a pipeline that critics warn could be environmentally catastrophic if it were to fail.

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