BISMARCK, N.D. (AP) — The chairman of the Standing Rock Sioux tribe says the U.S. Army Corps of Engineers plans to close the area where people have been camping for months to protest the Dakota Access oil pipeline.

Dave Archambault says he received a letter from the Corps on Friday which says all lands north of the Cannonball River will be closed Dec. 5.

Representatives from the Corps didn’t immediately return messages seeking comment and verification of the letter.

Archambault says the land to be closed includes the Oceti Sakowin camp, a sprawling encampment on Army Corps land about 50 miles south of Bismarck.

Archambault says the letter indicates a free speech zone will be allowed south of the Cannonball River. He says he’s disappointed in the Corps’ decision and is asking pipeline opponents to continue to fight the pipeline’s permitting process.