Canada once again relied on a long-standing treaty with the United States in its effort to keep the controversial cross-border pipeline open, warning of “significant” economic damage to both countries in case of closure.

Canadian Foreign Minister Melanie Joly said Line 5, a pipeline operated by Calgary-based Enbridge, was an important source of energy security.

The minister said in a statement: “Shutting down the pipeline will affect energy prices, at a time when global inflation makes it difficult for families to cover their expenses, these are unacceptable outcomes.”

She added that the government is concerned that the “domino effects” of the shutdown could extend to other parts of the Canadian economy and to communities on both sides of the border.

The 645-mile pipeline was built in 1953, running through Michigan and under the Great Lakes to supply nearly half of the oil needs in the Ontario and Quebec provinces, in addition to propane for the state of Michigan.

Canada’s defensive stance comes as a tribe of indigenous people in northern Wisconsin argues that Enbridge no longer has the right to cross their lands after the expiration of its easement rights.

The dispute represents the latest front in the battle against the pipeline that Canada says is vital for its energy needs.

Michigan Governor Gretchen Whitmer has previously raised concerns that the pipeline’s failure could cause catastrophic environmental damage. Enbridge says the pipeline is safe but will build a new tunnel to house the pipeline under the Mackinac Straits in the Great Lakes. The company has also promised to reroute Line 5 around the Bad River reservation in an attempt to resolve the confrontation “amicably” – a proposal strongly supported by Canada, Joly said.

Since November 2020, the governor of Michigan has been trying to shut down Line 5 for fear of an oil spill in the Mackinac Straits, where the pipeline crosses the Great Lakes.