U.S. military veterans were arriving on Thursday at a camp to join thousands of activists braving snow and freezing temperatures to protest a pipeline project near a Native American reservation in North Dakota.

Protesters have spent months rallying against plans to route the $3.8 billion Dakota Access Pipeline beneath a lake near the Standing Rock Sioux reservation, saying it poses a threat to water resources and sacred Native American sites.

State officials on Monday ordered activists to vacate the Oceti Sakowin camp, located on U.S. Army Corps of Engineers land near Cannon Ball, North Dakota, citing harsh weather conditions. Officials said on Wednesday however that they will not actively enforce the order.