The arrest was captured on camera by KGW8 on Monday.
Footage shows Marion County deputies repeatedly punching a local homeless man during an arrest on Monday outside of a Marion County search-and-rescue command center set up for two missing people.
Deputies can be heard telling the man to "stop resting."
The man, as he's being punched and beaten, insists several times he's not resisting.
"I'm not resisting! I'm not resisting," Kevin Straw, 28, repeatedly yells back at the deputies.
The American Civil Liberties Union on Oregon called for the Marion County Attorney's Office to launch an investigation into the incident.
"That video is disturbing. It's violent. Honestly, if that does not represent excessive use of force, I'm not quite sure what does," David Rogers, executive director of the Oregon ACLU, said.
Marion County deputy Ethan Griffith said Straw was arrested after he repeatedly entered the command post and disrupted search and rescue crews.
Griffith said Straw was making so much noise, rescuers couldn't hear commands to communicate with rescue and search personnel.
Deputies asked Straw to leave multiple times.
When he continued to refuse, deputies arrested him.
The Marion County Sheriff's Office said in a statement that Straw physically resisted, which required deputies to use force to subdue him.
On Saturday, deputies responded to reports Straw was screaming at passersby, talking about military special forces and cougars. When deputies met with Straw, he refused hep from the mobile crisis mental health response team, the department said.
Straw was ultimately evaluated by paramedics, cited for interfering with police and resisting, then taken for a mental health evaluation at the Psychiatric Crisis Center in Salem.