Protesters at the Standing Rock camp in North Dakota have been issued with an emergency evacuation order, with officials citing the upcoming winter as an excuse.
A spokesperson for the Morton County Sheriff's department told local media the evacuation order would mean supplies would be blocked from reaching the camp, including food.
But officials have distanced themselves from the statement, saying there won't be a blockade - but people will still be discouraged from entering the camp.
Vehicles thought to be heading to the camp will be stopped and warning they could be fined $1000 for an infraction, according to Reuters.
"That is the understanding that we had initially but we had to get that clarified," a spokesperson said.
"The governor is more interested in public safety than setting up a road block and turning people away."
People have gathered at the camp to protest the construction of the Dakota Access Pipeline, which would carry around 470,000 barrels of crude oil each day.
Members of the Standing Rock Sioux tribe say the project would affect their drinking water and put sacred Native American sites at risk.
North Dakota Governor Jack Dalrymple's evacuation order says harsh winter conditions have the "potential to endanger human life" and that the shelters in place at the camp haven't been properly inspected for safety.
"These persons are ordered to leave the evacuation area immediately, and are further ordered not to return to the evacuation area," he said in the order.
"Any action or inaction taken by any party which encourages persons to enter, re-enter, or remain in the evacuation area will be subject to penalties as defined in law."
Emergency services will also be no longer to provide care to those in the evacuation zone.
Standing Rock Sioux tribal leader David Archambault says the order is designed to "cause fear".
"[It's] a blatant attempt by the state and local officials to usurp and circumvent federal authority," he said.
"This is a clear stretch of state emergency management authority and a further attempt to abuse and humiliate the water protectors.
"The State has since clarified that they won't be deploying law enforcement to forcibly remove campers, but we are wary that this executive order will enable further human rights violations."
Violence has broken out at the protest on several occasions, including last week when police doused protesters in water cannon despite the freezing temperatures.
One woman could lose her arm after she says a law enforcement official threw an object at her that exploded.
Thousands of veterans are now heading to the camp to help defend the protesters, saying a "savage injustice" is being committed.
The veterans have been asked to bring body armour, gas masks, earplugs and shooting mufflers in preparation for any face-offs with law enforcement officials.
"We'll be standing alongside peaceful water protectors, who've endured violent attacks from the private security funded by DAPL and more brutality and arrests at the hands of militarised police and DAPL security," the Veterans for Standing Rock page says.
"If not us, who? If not now, when? Are you a hero? Are you honorable? Not if you allow this [to] be the United States."
The US army has also ordered protesters to evict the camp, citing federal regulations governing public lands.
While no one would be forcibly removed, the army did say anyone remaining on the land - including the protest camp - could be prosecuted for trespassing.