A June 2016 clash between Antifa and two neo-Nazi and white supremacist groups at the California State Capitol is being used as a prime example.
Politico reports that now both the Department of Homeland Security and the FBI have classified the group's violence as "domestic terror activity."
The report cites confidential law enforcement documents. It claims law enforcement is concerned that Antifa is using incidents like the violent clashes in Berkeley with white supremacist groups to broaden its recruiting and fundraising efforts.
"Any use of violence or threats of use of violence to coerce people into political change," Sac State professor and terrorism expert David Zuckerman said. "Certainly there are elements under the umbrella of Antifa that have done that."
Rallies on Aug. 27 in Berkeley and the Sacramento clash with the Traditionalist Worker Party, a white supremacist organization, resulted in multiple arrests of Antifa members.
But Zuckerman argues labeling all Antifa members as domestic terrorists isn't that simple. For one, he says, Antifa is not a traditional organization.
"It's a collection of folks and they're anarchists, and because they're anarchists, they don't organize," Zuckerman said.
Three people on the Antifa side of the Capitol clash were arrested on assault and riot charges, though their attorney claims they acted in self defense.
"Information that we have received certainly is that none of our three clients were aggressors," attorney Linda Parisi said. "They were acting in self defense."
Still, Zuckerman says Antifa members have demonstrated behavior that fits the legal definition of domestic terrorism.
"If people are threatening violence or using violence in order to coerce political change, they're terrorists," Zuckerman said.
The Department of Homeland Security declined an interview with FOX40, but instead issued a statement:
"DHS is concerned with extremism on any part of the ideological spectrum when it turns violent or threatening. We are actively engaged in reaching out to state and local stakeholders to provide analysis and warning regarding violent extremist activity."