Enbridge is also seeking state and federal permits to build a large utility tunnel under the straits to house a rebuilt section of Line 5. Michigan tribes and environmental groups are opposing the tunnel project, arguing it would disrupt potentially significant underwater archeological sites and that such fossil fuel infrastructure would contribute to global climate change. Related stories: Whitmer threatens profit seizure if Line 5 keeps pumping Tribes ramp up efforts to close Mackinac pipeline Enbridge settles with shipper after 2018 anchor strike Enbridge pledges to defy Whitmer shutdown order Canadian pressure mounts on Whitmer to back off Line 5 Michigan regulators approve Line 5 tunnel permits Line 5 closure would hike propane costs, consultant says Ohio, Louisiana argue against Line 5 shutdown in court Line 5 bent, deformed where anchors planned