North Dakota law enforcement will begin to block supplies from reaching protesters at a camp near the construction site of an oil pipeline project in an effort to force demonstrators to vacate the area, officials said on Tuesday.

Supplies, including food and building materials, will be blocked from entering the main camp following Governor Jack Dalrymple’s signing of an “emergency evacuation” order on Monday, Maxine Herr, a spokeswoman from the Morton County Sheriff’s Department, said. Activists have spent months protesting plans to route the $3.8 billion Dakota Access Pipeline beneath a lake near the Standing Rock Sioux reservation, saying the project poses a threat to water resources and sacred Native American sites.