Green Party presidential nominee Jill Stein waits to be introduced prior to a press conference at the National Press Club on Aug. 23 in Washington, D.C. Getty Images

Green Party presidential nominee Jill Stein is accused of committing a criminal act Tuesday after she spray-painted a bulldozer at a construction site for the Dakota Access Pipeline. Morton County Sheriff Kyle Kirchmeier said at a news conference Tuesday that Stein will likely soon be charged with trespassing and/or vandalism for the graffiti and her appearance at protest against the $3.8 billion oil pipeline, the Bismarck Tribune reported.

Stein, who came out last month against the pipeline, could be seen wielding a can of spray paint in a photo posted Tuesday to the Morton County Sheriff's Department's Facebook page. Stein spelled out "I approve this message" in red on a bulldozer blade after the activists invited her to write something, her spokeswoman told the Associated Press. Stein had camped there the night before.

Protests have been ramping up against the pipeline, which the Standing Rock Sioux Tribe alleges could contaminate its water supply and disrupt culturally significant sites, since early August. The sheriff's office told CNN the activists wounded Dakota Access Pipeline guards and dogs Saturday, an account the protesters refuted with stories of being pepper sprayed.

The demonstration Stein attended involved about 200 people, at least two of whom bound themselves to the construction vehicles, according to the AP. Nobody was arrested.

"We salute the courageous people of the Standing Rock Sioux reservation and their allies who are standing up to protect their land and our future on Earth from the poisonous fossil fuel industry and an economy that puts corporate profits over people and planet," Stein said in a news release last month. "The time is now to stop the destruction of our planet for short-term profits."

U.S. District Judge James Boasberg suspended some of the construction Tuesday while he considers another request from the tribe. His final decision could come by Friday.