"This pipeline must be stopped!" Sanders shouted to applause.
Sanders joined hundreds of activists, including members of the Standing Rock Sioux Tribe and other tribal nations, to rally against the Dakota Access Pipeline, which will move crude oil through four states from North Dakota to Illinois.
"Stop the pipeline, respect Native American rights and let us move forward to transform our energy systems away from fossil fuels," he said.
The Vermont senator also called on President Obama to "ensure that this pipeline gets a full environmental and cultural impact analysis."
The Standing Rock Sioux Tribe has sued to stop construction of the pipeline project. They argue it would cross through sacred sites and could pollute local drinking water. But last week, a federal judge denied the tribe's request to temporarily block the pipeline's construction.
Today, the company behind the controversial pipeline said in a statement that concerns over impact on water quality were "unfounded" and that no damage will be caused to sacred items, if they are found.
The company also said today it would meet with government officials but stayed mum on whether it would pause construction on the pipeline.
In an internal memo to staff, Chairman and CEO of Texas-based Energy Transfer Partners, Kelcy Warren, called on employees to contact their "elected representatives" and "tell them how important this project is to your livelihood," while slamming media "misinformation."
Warren also reiterated the company's commitment to "bring the Dakota Access Pipeline into operation."
"Concerns about the pipeline’s impact on the local water supply are unfounded," Warren wrote, adding that, "Dakota Access was designed with tremendous safety factors and redundancies, including compliance with and exceeding all safety and environmental regulations."
Warren also dismissed allegations of destruction to sacred sites.
"Multiple archaeological studies conducted with state historic preservation offices found no sacred items along the route," he wrote. "State archaeologists issued a ‘no significant sites affected’ determination in February on the North Dakota segment of the pipeline."
Tensions over the Dakota Access pipeline have mounted steadily throughout the summer, after the Standing Rock Sioux Tribe sued to temporarily halt construction, arguing that they were not adequately consulted.
Dave Archambault II, chairman of the Standing Rock Sioux Tribe responded to the CEO's memo, saying in a statement, "The Standing Rock Sioux Tribe will continue to explore all legal, legislative, and administrative options to stop construction of the Dakota Access Pipeline. It is unfortunate that the corporate world chooses to ignore the millions of people and hundreds of tribal nations who stand in opposition to the destruction of our lands, resources, waters, and sacred sites."
"Energy Transfer Partners has demonstrated time and time again that the bottom line for them is money," he added. "The bottom line for the Standing Rock Sioux Tribe is and will always be protecting our lands, people, water, and sacred sites from the devastation of this pipeline."
Jan Hasselman, an attorney for the Standing Rock Sioux Tribe told ABC News today that the tribe has filed an appeal and is hoping to make the government's request for a voluntary pause an enforceable requirement.
"It is a voluntary pause, so it is not enforceable by definition," Hasselman said, "We have asked the federal appeals court to make that request a court order."