An unprovoked attack on an Auckland bus driver earlier this week was "cruel", the union says.

A 39-year-old man has been arrested after allegedly punching and kicking a driver while on the bus on Monday afternoon.

The driver tried to kick the man off the bus after he boarded without tagging on and he allegedly attacked her, police said.

FIRST Union organiser for bus services Hayley Courtney told RNZ in a statement that the attack was totally unacceptable.

"No one should be made to feel unsafe at work, especially someone like a bus driver who's performing an essential service for their community while working long hours on relatively low wages with important responsibilities for passengers' wellbeing," she said.

Courtney said the union advised members not to police unpaid fares themselves due to the risk of abuse or assault.

"Drivers can record non-payment of fares, and it's the employer and Auckland Transport's responsibility to add additional security measures to ensure passengers are paying and not being abusive to drivers."

She said that anecdotally, attacks on drivers had increased in Auckland in the last five years.

"For many it does not feel like a safe city for a bus driver," she said.

Auckland Transport data from earlier this year showed assaults on bus drivers in Auckland had more than doubled in the last two years.

Courtney said some members have told the union they went to work worried that one day they would not come home.

"That is seriously concerning and requires coordinated action from employers, council and unions.

"It's not just a public transport issue but a wider social issue."

Courtney said the union wanted to see more Auckland Transport security at bus stops with repeated incidents of violence, more security guards on city buses, and a full rollout of drivers' protective screens an urgent priority.

Auckland Transport (AT) manager of public transport Rachel Cara said bus drivers played an important role in keeping the city moving and their safety was taken very seriously.

"Any act of violence or aggression towards them is completely unacceptable.

"Our buses all have CCTV cameras on-board and we have worked closely with police to make sure the attacker was brought to justice. We are also working with the bus operator to help the bus driver and give them the support they need."

Cara said this attack was shocking and AT recognised such an incident could cause concern for other bus drivers.

"We want them to feel safe in their place of work and we have a plan with our bus operators to roll out safety screens across the bus fleet. We also strategically deploy transport officers to de-escalate and deter violent behaviour where it is more likely to occur."

The 39-year-old man accused of the assault earlier this week will appear in Auckland District Court on Friday.