First Union spokesperson Hayley Courtney said many drivers were going to work fearing for their lives.
AT data from earlier this year showed assaults on drivers had more than doubled over the previous two years - from 24 assaults in 2022 to 51 in 2023.
Last year, a bus driver was stabbed in the ribs by a passenger, and in April, another driver was kicked and punched by someone who did not want to pay a fare in Ponsonby.
Courtney said the extreme incidents being reported were only the tip of the iceberg.
Auckland Transport group manager of public transport operations Rachel Cara said barriers would be on 80 percent of AT's fleet within the next two years.
She said drivers deserved to feel safe in their place of work and they were committed to rolling out the barriers as quickly as possible.
But Courtney said drivers were frustrated with the lack of urgency from AT and Auckland Council to put protective measures in place. As well as screens in drivers' cabins, she said the number of security officers at bus and train stations and on board dangerous routes needed to be increased.
She said the issue was affecting drivers nationwide, not just in Auckland.
Violent behaviour was also impacting passengers. Last week, RNZ reported a 17-year-old was threatened with a machete at Albany bus station. And in May, a 21-year-old stabbed another passenger in the neck on a bus in Newmarket. Weeks later, school students were warned to avoid the New Lynn bus and train station over fears of a mass brawl.
Courtney said drivers often felt pressured to step in, which could further escalate dangerous situations.
"We tell them to not engage. These drivers are not trained in self-defence - they are employed as bus drivers to transport the public, they are not employed as police officers."
About 40 AT-employed transport officers were warranted by police to respond to security threats or anti-social behaviour across its networks, and issue infringements for fare evasion.
AT spokesperson Rachel Cara said they were looking to recruit another 20 officers to support drivers.
