Hundreds of people protesting the Dakota Access Pipeline sat in at the U.S. Army Corps office this afternoon and are now marching to a rally at the White House.

Organizers want the U.S. Army Corps of Engineers, which is managing the pipeline project, to deny the permit for the controversial $3.7 billion Dakota Access pipeline to cross the Missouri River. Activists say the pipeline will destroy sacred historical sites and contaminate the sole source of water for the Standing Rock Sioux Tribe’s reservation.

The U.S. Army Corp of Engineers announced yesterday they are delaying an easement for the Dakota Access Pipeline project until it conducts further environmental review with the tribe, deferring a final decision. An easement is a right to cross or otherwise use someone else’s land for a specified purpose. According to the Army’s statement, they have “…determined that additional discussion and analysis are warranted in light of the history of the Great Sioux Nation’s dispossessions of lands, the importance of Lake Oahe to the Tribe, our government-to-government relationship, and the statute governing easements through government property.” The Army also reaffirmed the rights of all Americans to assemble and speak freely.

Energy Transfer Partners, the main company behind the pipeline, and its subsidiary, Sunoco Logistics Partners, subsequently filed papers asking the U.S. District Court in Washington, D.C. to intervene in the fight over the controversial project’s completion.

In addition to widespread protests against the president-elect, pipeline protests are happening around the country today. According to climate change activist group 350.org, which helped plan the D.C. protest, there are over 300 Dakota Access Pipeline protest events happening in all 50 states.

The coalition of environmental and social activist groups wrote on their Facebook event post: “The movement to stop Dakota Access is one of the most courageous stands against a fossil fuel project our country has ever seen, and it’s time for all of us to stand in solidarity with Indigenous communities on the ground.”