WASHINGTON — Shutting down Line 5 would cause Canada "grave harm" and violate its treaty rights, government lawyers argued Monday as the federal government rejoined the legal fray over the controversial cross-border oil and gas pipeline. An amicus brief filed with the U.S. Court of Appeals for the Seventh Circuit marked Ottawa's first foray into the ongoing legal dispute in Wisconsin, and its second since Michigan mounted a similar challenge in 2020. A Wisconsin court order issued in June gave Calgary-based Enbridge Inc. just three years — and not a day more — to reroute the pipeline around territory belonging to the Bad River Band of Lake Superior Chippewa. Enbridge's operations on Bad River territory "must cease" on June 16, 2026, regardless of whether the 66-kilometre detour around the reserve is complete, Wisconsin district court Judge William Conley ruled. Both sides are now appealing that decision.