Four 13-year-old boys have been charged in connection with a gang-style group attack aboard a TTC bus in Scarborough.

Toronto police said two of the boys face one count of assault, while the other two face two counts of assault.

The arrests follow the release of security camera footage from a local business showing at least a dozen youngsters pushing and assaulting two TTC employees outside a bus stopped near Kennedy and Merrian roads on Monday around 3:35 p.m.

While the TTC workers did not suffer life-threatening injuries, Jessica Davis, who saw what happened, says they appeared "really shaken up" and that the bus driver was "very upset."

"She was visibly, her hands were shaking," Davis said.

On Monday, police said they received reports of 10 to 15 youths attacking uniformed employees on the bus before fleeing the area.

Police said there was, in fact, a larger group of youths on the bus, but said investigators believe only four were directly involved in the assault.

The union representing TTC workers, ATU Local 113, is calling on the City and TTC to support the defense of its members during these repeated acts of violence.

"We need to put an end to these acts of violence and disrespect against transit workers," Marvin Alfred, president of ATU Local 113, told CTV News Toronto on Tuesday.

In a press release issued Tuesday, the union said "enough is enough," backing up the message that its members "shouldn't have to go to work every day in fear of their lives."

The swarming-style attack comes just a couple of days after a TTC operator was shot with a BB gun in Scarborough on Saturday night.