The Fury actor launched the four-year project, titled HE WILL NOT DIVIDE US, with 18-year-old Jaden Smith last Friday (20Jan17).

Shia, 30, and Jaden asked members of the public to protest against the newly installed U.S. leader, Donald Trump, for the duration of his first term as president by chanting "He will not divide us" in front of a camera fixed outside New York City's Museum of the Moving Image, which will be live streamed.

According to TMZ.com, New York Police Department (NYPD) officers have been stationed at the protest since Monday (23Jan17), and were quick to move in when Shia allegedly grabbed the scarf of a man who said something that angered him.

The Transformers star is said to have scratched the man in the process of grabbing him, leading to him being led away in handcuffs.

His fellow protesters told TMZ.com: "Shia took a hit for us. There were all these Nazis here, he came out and tried to protect us."

Jaden also took to his Twitter page to reference the incident with the simple hashtag "#FreeShia".

The New York Post's gossip column Page Six adds that a previous video from the site showed a man going up to hug Shia before shouting, "Hitler did nothing wrong."

Shia is then seen apparently shoving the man, before the camera panned away. However, it's not clear whether or not this is the incident for which the actor was arrested.

Shia is now being held at the 114th Precinct Station house, but has not yet been booked, according to TMZ. The outlet adds he is looking at a misdemeanor assault charge.

The latest incident follows Shia’s angry confrontation with a white nationalist on Sunday (22Jan17). After the man positioned himself in front of the camera and shouted "We must ensure the existence of the white people as a race," Shia responded by screaming "he will not divide us" in the interloper's face repeatedly and barging him away from the camera.

The phrase that caused Shia’s reaction is similar to an infamous white supremacist slogan known as the Fourteen Words.