“I don’t think that this country ever anticipated that people being arrested for insignificant infractions would be thrown into an unmarked van by folks holding long guns and rifles,” the 25-year-old protester's attorney said.

PITTSBURGH (KDKA) – Pittsburgh Mayor Bill Peduto said he’s “livid” about plainclothes police putting a protester in an unmarked white van and whisking him away. The mayor said he won’t tolerate the tactic in the future.

“It is hard to find the words for how livid I was after seeing the online videos of the disturbing arrest at Saturday’s protest. I have taken the time to review all the video and information that has been made available to me,” Mayor Peduto said in a statement.

But Monday protest organizers again called for his resignation.

“You and your colleagues violated our constitutional rights and left your citizens — mind you, the people that you are supposed to keep safe — traumatized,” said A.D. Bagheera, one of the protest organizers.

Twenty-five-year-old Mathew Cartier is charged with disorderly conduct and obstruction of highways for allegedly moving ahead of demonstrators and blocking traffic. Police Sunday called the method of his arrest a “surgical maneuver.”

“That was a calculated movement that was done to remove somebody from the event and make sure that everything was safe,” Chief Scott Schubert said.

Pittsburgh Mayor Bill Peduto sat down one-on-one with KDKA’s Meghan Schiller and said he was told “that there were tactical reasons why this would provide the least negative impact.”

WATCH: KDKA’s Meghan Schiller Talks One-On-One With Mayor Peduto

“Even if that was true, it didn’t answer the question of common sense,” said Mayor Peduto.

But Cartier’s attorney, public defender Lisa Middleman, called the tactic excessive and for the charges against Cartier to be dropped.

“I don’t think that this country ever anticipated that people being arrested for insignificant infractions would be thrown into an unmarked van by folks holding long guns and rifles,” she said.

(Photo Credit: Allegheny County Jail)

But while Vic Waczak of the American Civil Liberties Union says the optics of Cartier’s arrest look bad, the arrest is legal if police had probable cause.

“If they did, whether they did it quickly, whether they did it wearing uniforms or not wearing uniforms is not going make it unconstitutional, but it is definitely creepy,” he said.

And Walczak urged the police not to deploy the maneuver in the future.

“It feels like something rogue happening in the Soviet Union. So whether or not it’s actually constitutional — really would urge police to rethink the tactic,” he said.

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Allegheny County District Attorney Stephen Zappala released a statement saying Cartier arrest should “be a summary offense at best” and should be handled by police in a summary hearing.

DA Zappala’s statement reads in full:

“In 2005, I requested that the Pennsylvania Supreme Court change the rules of criminal procedure to allow for more low level offenses to proceed by summons, the equivalent of being written a traffic citation, rather than by arrest.

“On Saturday, Pittsburgh Police, directed by the Public Safety Director and the Mayor, chose to proceed by arrest and criminal complaint on charges that should have been handled via summons.

“While I appreciate the right to free speech and peaceful protest as afforded by the constitution, I also appreciate the inconvenience and potential danger created by blocking access to roadways, intersections and possibly hospital entrances.

“Pending the review of body worn camera footage which my office obtained earlier today, this matter appears to be a summary offense at best and should be handled by the Pittsburgh Police Department in a summary hearing.”

The president of Black, Young & Educated said Peduto has not reached out to her organization and has never attended a Civil Saturday protest.

“He has been vilifying protesters since the beginning of the protests in the summer and standing at the defense of police officers. We clearly see where our Mayor stands in this movement, and we’d like to change that,” said Treasure Palmer, president of the organization.

WATCH: KDKA’s Jennifer Borrasso Has More

Another member of the organization said that Public Safety has not reached out to their organization since June 27.

“It is completely disgusting and heartbreaking how a city that I grew up in can blatantly lie and attempt to vilify a collective group of young adults who are trying to better the future for Black youth and Black families in this city in order to cover their Civil Affairs’ unit subpar job performance,” said Nicholas Anglin, CEO of Black, Young & Educated.

But Mayor Peduto says the organizers have refused to meet with city officials.

“Our officers have reached out to them to have meetings, to sit down and try to find common ground,” Mayor Peduto told KDKA’s Meghan Schiller. “They have refused to meet.

“Our task force for police reform has invited them to the table to add their voice to the other voices, and the youth representatives that are already on the task force, they have refused to come to the table. If their activity is for social change simply by getting into the street and protesting, and not trying to work constructively, that is not a behavior I will condone.”

The Pittsburgh Community Task Force On Police Reform issued a statement, saying:

“The Pittsburgh Community Task Force on Police Reform strongly condemns the actions of a non-uniformed group of Pittsburgh police officers at the corner of Forbes Ave. and S. Bouquet St. on August 15. We have heard from countless members of our community, including law enforcement officers and those exercising their First Amendment rights to protest, who are desperate for these policing tactics to change, and to change now. As we continue our work as a Task Force, we pledge to address such police tactics in our final report, and we call on Mayor Peduto, Public Safety Director Hissrich, and Chief Schubert to immediately address this incident and provide full transparency to the community. We also call on the Pittsburgh Bureau of Police and protest leaders to work together to ensure the safety of everyone involved.”

The Citizen Police Review Board has an open inquiry into the incident.