CANNON BALL, N.D.—Protesters who celebrated a major victory in their push to reroute the Dakota Access oil pipeline vowed to remain camped on federal land as they wait to find out whether President-elect Donald Trump might seek to overturn a decision that delayed the $3.8 billion project.

The American Petroleum Institute, which represents the U.S. oil and natural gas industry, urged Trump to make approval of the disputed pipeline a “top priority” once he takes office next month, but a Trump spokesman on Monday offered few clues about how the incoming president might address the matter.

The Army Corps of Engineers on Sunday denied a permit for the pipeline to cross under the Missouri River in southern North Dakota near the Standing Rock Sioux Reservation. The tribe believes the 1,200-mile pipeline to transport North Dakota oil to a shipping point in Illinois threatens drinking water and cultural sites.

The segment under Lake Oahe is the only remaining big chunk of construction on the four-state pipeline that also crosses through South Dakota and Iowa.

“I am hopeful President-elect Trump will reject the Obama administration’s shameful actions to deny this vital energy project,” American Petroleum Institute President and CEO Jack Gerard said in a statement late Sunday.

Trump supports construction of the pipeline, spokesman Jason Miller told The Associated Press on Monday, but Miller wouldn’t say whether Trump would reverse the Corps’ decision.

“We will review the full situation when we’re in the White House and make the appropriate determination at that time,” Miller said.

The uncertainty of what Trump will do is keeping many supporters in the camp despite winter conditions.

“The whole world is watching,” said Miles Allard, a member of the Standing Rock Sioux. “I’m telling all our people to stand up and not to leave until this is over.”

Pipeline opponents have camped for months near the pipeline route in North Dakota. Hundreds of people at the Oceti Sakowin, or Seven Council Fires, encampment cheered and chanted “mni wichoni” — “water is life” in Lakota Sioux — on Sunday when they learned of the Corps’ decision.

The uncertainty of what Trump will do is keeping many supporters in the camp despite winter conditions.

The company constructing the pipeline, Dallas-based Energy Transfer Partners, slammed the Corps’ decision as politically motivated and alleged that President Barack Obama’s administration was determined to delay the matter until he leaves office.

“The White House’s directive today to the Corps for further delay is just the latest in a series of overt and transparent political actions by an administration which has abandoned the rule of law in favour of currying favour with a narrow and extreme political constituency,” the company said in a statement Sunday night.

Assistant Secretary for Civil Works Jo-Ellen Darcy said in a news release that her decision was based on the need to consider alternative routes for the pipeline’s crossing. Her full decision doesn’t rule out that it could cross under the reservoir or north of Bismarck.

“Although we have had continuing discussion and exchanges of new information with the Standing Rock Sioux and Dakota Access, it’s clear that there’s more work to do,” Darcy said. “The best way to complete that work responsibly and expeditiously is to explore alternate routes for the pipeline crossing.”

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North Dakota’s leaders criticized the decision, with Gov. Jack Dalrymple calling it a “serious mistake” that “prolongs the dangerous situation” of having several hundred protesters who are camped out on federal land during cold, wintry weather. U.S. Rep. Kevin Cramer said it’s a “very chilling signal” for the future of infrastructure in the United States.

U.S. Secretary for the Interior Sally Jewell said in a statement that the Corps’ “thoughtful approach . . . ensures that there will be an in-depth evaluation of alternative routes for the pipeline and a closer look at potential impacts.”