Yesterday (August 11), approximately 200 protestors from the Oceti Sakowins (commonly known as the Sioux people)—joined by “Divergent” actress Shailene Woodley—blocked crews constructing the $3.7 billion Dakota Access Pipeline set to run through their land. Though the group remained peaceful, the Morton County Police Department arrested 12 for disorderly conduct or criminal trespass, reports the Associated Press.

Tribal members have been protesting the 1,172-mile long pipeline for months. Earlier this month, they delivered a petition with more than 160,000 signatures to the White House, demanding an end to its construction. They claim the Dakota Access will contaminate their water and damage land. It will transport 450,000 barrels of crude oil a day from the Bakken Shale Formation in North Dakota through South Dakota and Iowa to Illinois.

The Army Corps of Engineers approved the last permits needed to begin work on the pipeline in July, resulting in a lawsuit from the Oceti Sakowin. Non-Native landowners in Iowa have launched lawsuits against the state, asserting it cannot use eminent domain law to forcefully buy their land for a private company.