BURNABY, B.C. - An assault investigation is underway after a passenger kicked a door and spat on a bus driver in Burnaby Tuesday afternoon.

According to Metro Vancouver Transit Police, the passenger became irate, then violent, when he was asked repeatedly to move behind the red line near the driver.

Jane Guidoriagao was on board the bus with her nine-year-old son when she noticed the man near the driver becoming aggressive as the driver asked the man to step back.

"That's when I noticed something was going to happen," Guidoriagao told CTV News Wednesday.

Guidoriagao took a six-second video that shows the man aggressively kicking the bus door before spitting at the driver. He then steps onto the street, near Canada Way and Hardwick Street, and walks off.

"I was scared for my fellow companions that were on the bus, especially the driver. And for my safety and for my son at the same time," Guidoriagao said. The bus driver was not physically injured in the attack.

"He was probably in shock. He was calm," Guidoriagao said. "Treating a bus driver with disrespect and spitting on their face. It's idiotic and unnecessary."

She says the driver had let the man on for free a few minutes before the attack.

Transit police say they are investigating the attack as an assault and are looking closely at Guidoriagao's video.

"Nobody deserves to be assaulted just trying to do their job. When it does occur it’s absolutely something that we take seriously," said Sgt. Clint Hampton with transit police.

The driver had pulled the bus over when the attack happened.

Transit police have interviewed several witnesses who were on the bus, but are asking others who may have information to come forward.

Video of the attack is also putting the safety of bus operators back in the spotlight, with bargaining between Coast Mountain Bus Company and the union representing bus drivers back underway in Surrey Wednesday.

"A graphic scene like that just gives you an indication of the kind of conditions our members face every day. It's not simply just driving a bus, it's dealing with the public, it's dealing with people who are irate," Gavin McGarrigle with Unifor told reporters Wednesday.

Bus drivers in Metro Vancouver are threatening to strike starting Friday if a deal isnt reached by Thursday night.

According to the union, issues on the table include overcrowding, wages and working conditions.

"I think a video like that really illustrates how tough the conditions are for drivers out there," McGarrigle said.

Guidoriagao, who regularly uses transit, says she has had a tough time explaining the incident to her young son and is now worried for her own safety.

"I'm scared now. What if it’s going to happen again," she said. "I fear for myself and everyone else as well."

Transit police say they are checking to see if the bus where the incident happened captured any video surveillance of the attack.

A suspect has not been arrested or identified.