Environmental groups are asking President Obama to intervene in the construction of a controversial oil pipeline project in North Dakota.

In a letter to Obama on Thursday, 31 green groups said the White House should deny and revoke the permits necessary to build the Dakota Access pipeline, a 1,168-mile project that would carry 450,000 barrels of Bakken crude oil from North Dakota to Illinois.

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The appeal to the White House comes after the Standing Rock Sioux tribe of North Dakota sued the Army Corps of Engineers over its approval of the project.

The tribe contends that federal regulators didn’t give tribal leaders the option to assess the pipeline’s impact on cultural sites or sensitive environmental locations and is asking a judge to halt construction until it can do so. The Corps told a federal judge on Wednesday that it had tried to consult the tribe but was rebuffed.

Thursday’s letter, from groups like the Sierra Club, Honor the Earth, 350.org and others, including several from the Midwest, opens a new front in the fight against the pipeline. The groups want Obama to deny new permits for the project, as he did with the Keystone XL pipeline project last year, and remove existing permits issued by the Army Corps.

The groups aligned their arguments with those of the tribe, saying the pipeline threatens the tribe’s ancestral lands and its current reservation.

"If there were to be a spill — which history has taught us is not a question of ‘if’ but ’when’ — it would constitute an existential threat to the tribe’s culture and way of life," the groups wrote. "The pipeline poses significant threats to the environment, public health, and tribal and human rights."

The letter comes as greens, tribal-rights groups and anti-fossil fuel organizations turn their focus to this new pipeline. Around 20 people have been arrested in North Dakota during protests against the pipeline, and allies of the tribe rallied against it in Washington, D.C., on Wednesday.

Sen. Bernie Sanders Bernie SandersNYT editorial board remembers Ginsburg: She 'will forever have two legacies' Two GOP governors urge Republicans to hold off on Supreme Court nominee Sanders knocks McConnell: He's going against Ginsburg's 'dying wishes' MORE (I-Vt.) came out against the pipeline on Thursday, saying, “Regardless of the court’s decision, the Dakota Access pipeline must be stopped.

“As a nation, our job is to break our addiction to fossil fuels, not increase our dependence on oil,” he said in a statement. “I join with the Standing Rock Sioux Tribe and the many tribal nations fighting this dangerous pipeline.”