Opponents of Enbridge's new Line 3 project have asked a federal court to halt construction of the $2.6 billion pipeline, saying the U.S. Army Corps of Engineers failed to adequately address several environmental issues when it approved a key water quality permit.

Two Minnesota Ojibwe bands and two environmental groups on Thursday sued the Army Corps in U.S. District Court for the District of Columbia, asking for a preliminary injunction to stop construction on the oil pipeline across northern Minnesota.

"The Corps' issuance of the permit authorizing the pipeline violates multiple federal laws and treaties, harming plaintiffs and their members," the complaint said.

The suit was filed by the Red Lake Band of Chippewa, the White Earth Band of Ojibwe, the Sierra Club and the Indigenous environmental group Honor the Earth.

They are represented by Earthjustice, a nonprofit law group that has represented the Standing Rock Sioux tribe in its longstanding legal battle with the Army Corps over the Dakota Access oil pipeline in North Dakota.

To get a court injunction, the plaintiffs must show that the Corps' decision — and thus Line 3's construction — is causing them irreparable harm. They also must show their case will prevail on its merits, which can be a high legal bar.

The Army Corps declined to comment Monday, saying it had yet to review the lawsuit.

Enbridge said it's reviewing the suit, and noted that tribes were consulted by the Army Corps during the permitting process.

"The Line 3 Replacement Project has passed every test through six years of fact and science based regulatory and permitting review," Enbridge said in a statement.

The Corps on Nov. 23 issued its "404 permit" for the discharge of dredged and filled material into U.S. waters during Line 3's construction.

The permit was the last major approval Calgary, Alberta-based Enbridge needed to begin construction on the 340-mile pipeline, which navigated the state and federal regulatory process for six years. Construction began early this month.

The suit argues that under federal law, the Army Corps' jurisdiction doesn't just cover environmental impacts of construction. The Corps failed to evaluate the risks and impacts of oil spills, which is particularly important given the nature of the oil that Enbridge will transport, plaintiffs allege.

Line 3 will carry thick Canadian oil that sinks in water and is harder to contain during a spill.

The suit also contends that the Army Corps didn't properly evaluate the pipeline's impact on climate change and that the agency should have conducted its own environmental impact statement on the pipeline.

The Corps also failed to fully assess Line 3's impacts on tribal treaty rights, the suit argues. While new Line 3 would only cross one of seven Ojibwe reservations — Fond du Lac — it goes through lands where Indians have treaty rights to hunt, gather and fish.

Line 3 already employs more than 3,000 workers, one of the largest construction projects in Minnesota in recent years. Enbridge expects to complete the pipeline by 2021's fourth quarter.

Line 3 was reapproved in February by the Minnesota Public Utilities Commission (PUC), the state's primary pipeline regulator. The PUC's first approval in 2018 was voided when the Minnesota Court of Appeals shot down the state's original environmental impact statement for the pipeline.

Ojibwe bands and environmental groups have challenged the PUC's approval of Line 3 at the state appeals court, and they are expected to soon ask for a stay to halt construction.

Environmental groups and some Indian bands have said the pipeline — which follows a new route — will open a new region of pristine waters to the prospect of oil spills, as well as exacerbate climate change by allowing for more oil production. Enbridge has said the new pipeline is a critical safety enhancement. The current Line 3 is so corroded it's running at only half of capacity. The new pipeline would restore full oil flow.

Mike Hughlett • 612-673-7003