BISMARCK, N.D. (AP) – The chairman of the Standing Rock Sioux Tribe says he has contacted the White House and met with North Dakota’s senators in an effort to halt construction of a $3.8 billion, four-state oil pipeline.

David Archambault II says he met Wednesday with North Dakota Sens. John Hoeven and Heidi Heitkamp to “express concerns” about the Dakota Access pipeline that will cross the Missouri River just north of the Standing Rock reservation and also travel through South Dakota and Iowa to Illinois.

Archambault says he is calling for peaceful protests of the pipeline. Archambault and others have been arrested in the past week for interfering with construction in southern North Dakota.

North Dakota transportation officials on Wednesday closed a several-mile stretch of Highway 1806 because of the protest along the road.