During a Monday demonstration, activists asked Ms Stein to leave a message at the protest, after which she wrote "I approve this message" across the blade of a bulldozer in red spray paint, according to campaign spokesperson Meleiza Figueroa.
She also tweeted: "The Dakota Access Pipeline is vandalism on steroids".
The Standing Rock Sioux Tribe and another neighboring tribe oppose the construction of the pipeline, which the Standing Rock Sioux Tribe says would disrupt sacred land and affect its people's water supply.
The Bismarck Tribune also reported that "some protesters were on horses, masks, and some carrying hatchets and wearing goggles". "No arrests were made at the time". She claimed the school closings have targeted "communities of color" and that those communities are "not being served" because students are being reassigned to schools they can't get to. It said authorities were investigating the protest, which it called a "criminal act".
A ruling is expected by Friday on the tribe's challenge of the U.S. Army Corps of Engineers' decision to grant permits to the Dallas -based operators of the $3.8 billion Dakota Access Pipeline, which will cross North Dakota, South Dakota, Iowa and IL.
"The pipeline will carry up to 570,000 barrels of highly polluting Bakken crude oil per day. Energy Transfer Partners hopes to see the asset online by fourth quarter 2016".
They're awaiting a critical ruling from a federal judge on the Standing Rock Sioux tribe's request to block the $3.8 billion pipeline over environmental concerns.
What followed the blatant desecration of sacred sites was a clash between largely Native American protesters and construction workers.
He noted that he saw very few law enforcement personnel near the protest site Wednesday and said he's appealing to protesters to remain "peaceful and prayerful".
"Yes I would, most definitely", said Derrick Young.
Just days before, protesters had been attacked by company owners who brought attack dogs and used pepper spray.
There's an old joke about how much effort it takes to show up on TV.
Dr. Jill Stein was one of several people arrested in 2012 during the protests in Wood County over the controversial Keystone XL pipeline.