Hundreds of United States military veterans vow to defend the Standing Rock protest camp and march through a winter blizzard to the scene of recent clashes with state police and the national guard just outside of the Lakota Sioux reservation of Standing Rock, North Dakota, December 5, 2016.

The controversial Dakota Access pipeline will receive a permit from the U.S. Army Corps of Engineers to allow construction of the $3.7 billion project to be completed, according to North Dakota Senator Heidi Heitkamp.

The pipeline at the center of months of protests that has galvanized Native Americans and environmental activists. It would carry oil from North Dakota, through South Dakota and Iowa to be shipped out of Illinois.

Members of Congress were notified of the decision earlier on Tuesday, according to two sources with knowledge of the decision.

The sources said no easement had been formally granted as of Tuesday night but that one "could come as soon as Wednesday or Thursday."

"For months, North Dakotans have been on edge over the construction of the Dakota Access Pipeline and the protests surrounding it," Heitkamp told NBC News late Tuesday. "Now that the Acting Secretary of the Army has directed the Army Corps of Engineers to issue an easement to complete the project, we know construction will move forward."

Last week, Trump signed orders clearing roadblocks for The Dakota Access pipeline and the Keystone XL pipeline, which would bring oil from Canada to Nebraska.

The Dakota Access pipeline was largely finished except for a section under North Dakota's Lake Oahe, near a Sioux Tribe that has disputed construction because they say it could pollute their water supply and would disrupt key cultural sites.

After months of clashes with protesters — that occasionally turned violent — opponents of the pipeline claimed victory in December when the Army Corps of Engineers denied Energy Transfer Partners a permit to cross the Missouri River.

The Army Corps of Engineers — which has jurisdiction over the land where the pipeline would cross — agreed to consider alternative routes and begin an environmental impact study (EIS), a process that could take months.

Trump's move doesn't order construction of the pipeline, but does require expedited consideration of permit requests.

More from NBC News:

Pipeline protesters decry North Dakota Bills that 'criminalize' protests

Dakota protesters say Belle Fourche oil spill 'validates struggle'

Despite victory, Dakota Access protesters wary of future



December's reprieve proved to be a short victory for the Standing Rock Sioux tribe, whose reservation sits a half-mile from where the pipeline would cross, and for the thousands of activists who have protested at the Oceti Sakowin Camp in Cannon Ball, North Dakota.

In a statement to NBC News, Standing Rock Sioux Chairman Dave Archambault II said granting an easement now would effectively "abandon the EIS" and would amount "to a wholly unexplained and arbitrary change based on the president's personal views."

Archambault said the tribe would fight the easement in court.

"We stand ready to fight this battle against corporate interest superseding government procedure and the health and well-being of millions of Americans," he added.

Members of the Standing Rock Sioux tribe see the pipeline as both an environmental and cultural threat to their homeland. They say an oil spill would permanently contaminate the reservation's water supply and that construction of the pipeline would destroy sacred sites where many of their ancestors are buried.

Energy Transfer Partners, the Dallas-based company funding the project, says it will bring millions of dollars into local economies and create an estimated 8,000 to 12,000 construction jobs.

A spokesperson for Energy Transfer Partners was not immediately available for comment.

In an interview with NBC News just days after the presidential election, Energy Transfer Partners CEO Kelcy Warren said he "was 100 percent sure that the pipeline" would be approved by the Trump administration.

A federal judge is currently presiding over litigation between the tribe, Energy Transfer Partners and the government. The next hearing is scheduled for Feb. 6.