The company behind the construction of the Dakota Access Pipeline, Energy Transfer Partners, needs an easement, or permission, from the Corps in order to drill under Lake Oahe — on the Missouri River — to finish the oil pipeline along its proposed route.

Energy Transfer Partners had been waiting on a decision from the Army Corps since September when they launched a review of a requested easement.

Monday’s letter from the Army Corps to the Standing Rock Sioux Tribe, Dakota Access LLC, and Energy Transfer Partners said construction “cannot occur because the Army has not made a final decision on whether to grant an easement.” It said they would work with the Standing Rock Sioux on a timeline “that allows for robust discussion and analysis to be completed expeditiously.”