North Dakota's governor has signed an executive order for an "emergency evacuation" of demonstrators who have been camped out for months in opposition to a contentious oil pipeline.

In a statement issued Monday, Gov. Jack Dalrymple said hundreds of people who have been camped on land north of the Standing Rock Sioux Tribe's reservation must leave immediately and not return.

According to that executive order, "Morton County is currently experiencing severe winter weather storm conditions, and it is anticipated harsh winter conditions will continue until next spring."

"Winter conditions have the potential to endanger human life, especially when they are exposed to these conditions without proper shelter, dwellings, or sanitation for prolonged periods of time."

'Menacing action'

The Standing Rock Sioux Tribe dismissed the governor's reasons for issuing the order.

"This state executive order is a menacing action meant to cause fear," said Dave Archambault, chair of the tribe. 

"The governor cites harsh weather conditions and the threat to human life ... the most dangerous thing we can do is force well-situated campers from their shelters and into the cold."

​"Enough is enough," said Tara Houska, an Anishinaabe lawyer who has been in the camp for months. 

"These are Lakota, Dakota and Nakota lands. These are Indigenous lands. We've been pushed around by governments since they first arrived on our shores and this should not be the conversation in 2016."

Houska said later on social media that the governor's move was less about clearing the camps and more about cutting off emergency services, like ambulances, for demonstrators.

Army Corps issues eviction

The governor's executive order follows an eviction notice issued by the U.S. Army Corps of Engineers on Friday.

However, the Corps says it won't forcibly remove people from a massive camp used by those opposed to the Dakota Access pipeline, though it's still unclear how the eviction notice will be enforced.

The camp — called Oceti Sakowin — is just north of the Standing Rock Sioux Tribe reservation, where Texas-based Energy Transfer Partners has been trying to complete the contentious Dakota Access pipeline. If finished, the $3.8-billion U.S. pipeline will carry crude oil south to Illinois from northern North Dakota.

On Friday, the Army Corps sent a letter to the Standing Rock Sioux Tribe stating that land north of the reservation would be closed to the public as of Dec. 5 and that a "free speech zone" would be established nearby where people could freely demonstrate.

"The Army Corps of Engineers is seeking a peaceful and orderly transition to a safer location, and has no plans for forcible removal," read a news release issued on Nov. 27.

"Those who remain will be considered unauthorized and may be subject to citation under federal, state, or local laws."

Lawsuit launched

The Corps also said "more dangerous groups have joined this protest and are provoking conflict in spite of the public pleas from tribal leaders."

But people in the camp — and their many supporters — say it is heavily armed state and county police who are the real aggressors.

More than 500 people have been arrested in demonstrations since the summer and one woman nearly lost an arm when she was injured during a clash with police on Nov. 20.

The conflict that night is now the subject of a lawsuit launched by a group of lawyers called the Water Protector Legal Collective, which has been providing legal assistance to people involved in the demonstrations.

Dakota pipeline protest Nov 20

Demonstrators face off with police near the Standing Rock Indian Reservation on Nov. 20.

The group filed a class-action lawsuit on Monday, seeking an injunction against the Morton County Sheriff's Department and other police forces who were present on Nov. 20, which the lawyers accuse of using excessive force — and employing "impact munitions such as rubber bullets and lead-filled "beanbags," water cannons and hoses, explosive tear gas grenades and other chemical agents against protesters."

The Morton County Sheriff's Department has denied that its officers used explosives, instead blaming demonstrators themselves. Sheriff Kyle Kirchmeier was also critical of the Corps's announcement, telling The Associated Press that the Corps "is basically kicking the can down the road, and all it is doing is taking the liability from the Corps and putting it on [the Standing Rock Sioux Tribe]."  

Widespread support

The Sioux's fight against the Dakota Access pipeline has garnered support from around the globe, with thousands of Indigenous and non-Indigenous people making the pilgrimage to North Dakota.

First Nation communities across Canada have also shown solidarity through rallies, round-dances and fundraisers. Manitoba NDP MLA Wab Kinew has raised the issue in the province's legislature.

Kristen Wiig Standing Rock

Kristen Wiig wears a 'Stand with Standing Rock' T-shirt during the close of Saturday Night Live on Nov. 19. (NBC)

Celebrities that include singer Neil Young and actors Susan Sarandon, Jane Fonda and Mark Ruffalo have spoken out about the issue or visited Standing Rock. Actor and comedian Kristen Wiig wore a "Stand with Standing Rock" T-shirt during the close of Saturday Night Live on Nov. 19

Actor Shailene Woodley was arrested during her time in the area in October.