Enbridge Inc.’s battle with Michigan escalated on Friday as the governor took new legal action to shut down a key pipeline that supplies Central Canadian refineries.

Governor Gretchen Whitmer filed a complaint in Ingham County Circuit Court seeking to “revoke and terminate” an 1953 easement that allows Enbridge to operate under the Straits of Mackinac, which connect Michigan’s upper and lower peninsulas. Line 5 is a key conduit of crude for Canadian refineries in Ontario and Quebec.

“Enbridge’s Line 5 is a grave and unreasonable risk to the state’s residents and natural resources and requires the pipeline to be shut down 180 days from now, on May 12, 2021,” the state said in a release Friday. Enbridge didn’t respond to an email seeking comment. The shares erased earlier gains following news of the latest legal action and were down 0.8% at C$37.69 at 1:47 p.m. in Toronto.

Enbridge has been in a long-running battle over the pipeline with Michigan’s Democratic administration, which views the line as an environmental threat to the Great Lakes. In June, a judge ordered Enbridge to temporarily halt operations of Line 5 amid concern about possible damage.

The temporary shutdown of both the eastern and western segments prompted Imperial Oil Ltd. to warn of possible production cuts at its Sarnia and Nanticoke refineries. While Michigan governor wants to shut the pipeline, Enbridge seeks to make the line more secure by building a tunnel under the strait to house the line.

Line 5 carries as much as 540,000 barrels a day of Canadian light crude oil, light synthetic crude, and natural gas liquids from Superior, Wisconsin, to Sarnia, Ontario, where it links to a pipeline that runs as far north as Montreal.