Opponents of the long-stalled Keystone XL oil pipeline asked a federal court on Friday to declare that Donald Trump acted illegally when he issued a new permit for the project in a bid to get around an earlier court ruling.
In November, US district judge Brian Morris ruled that the Trump administration did not fully consider potential oil spills and other impacts when it approved the pipeline in 2017.
Mr Trump's new permit, issued last week, is intended to circumvent that ruling and kick-start the proposal to ship crude oil from the tar sands of western Canada to US refineries.
White House officials have said the presidential permit is immune from court review. But legal experts say that is an open question, and the case could further test the limits of Mr Trump's use of presidential power to get his way.
Unlike previous orders from Mr Trump involving immigration and other matters, his action on Keystone XL came after a court already had weighed in and blocked the administration's plans.
"This is somewhat dumbfounding, the idea that a president would claim he can just say, 'Never mind, I unilaterally call a do-over,"' said William Buzbee, a constitutional scholar and professor at Georgetown University Law Centre.
Opponents say burning crude from the tar sands of Western Canada would make climate change worse. The $8bn (£6.1bn) project's supporters say it would create thousands of jobs and could be operated safely.
The line would carry up to 830,000 barrels (35 million gallons) of crude daily along a 1,184-mile path from Canada to Nebraska.
Stephan Volker, an attorney for the environmental groups that filed the lawsuit on Friday, said Mr Trump was trying to "evade the rule of law" with the new permit.
"We have confidence that the federal courts—long the protectors of our civil liberties—will once again rise to the challenge and enforce the Constitution and the laws of this land," Mr Volker said.
The White House said in a statement that under the new order, federal officials would still conduct environmental reviews of the project.
However, officials said those would be carried out by agencies other than the State Department, which under Mr Morris' November order would have been forced to conduct another extensive study that could have taken months to complete.
TransCanada spokesperson Matthew John said the administration's action "clearly demonstrates to the courts that the permit is (the) product of presidential decision-making and should not be subject to additional environmental review."
Friday's lawsuit was filed in Mr Morris' court, meaning he is likely to get the first opportunity at addressing the legality of Mr Trump's new order. Judges typically do not respond favourably to perceived end runs around their decisions, said Carl Tobias with the University of Richmond law school.
Another legal expert, Kathryn Watts at the University of Washington, said it is unclear where the case will lead. Mr Trump's permit wades into "uncharted, unsettled" legal territory, she said.
Earlier this week, a court granted the tribes' request to intervene in an appeal of Mr Morris' November ruling that was filed by TransCanada. That case is pending before the 9th US Circuit Court of Appeals.
Tribal officials contend a spill from the line could damage a South Dakota water supply system that serves more than 51,000 people including on the Rosebud, Pine Ridge and Lower Brule Indian Reservations.
An existing TransCanada pipeline, also called Keystone, suffered a 2017 spill that released almost 10,000 barrels (407,000 gallons) of oil near Amherst, South Dakota.
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