The spokesperson, whose son was also at the party, said the driver replied that he had not done that before and seemed wary, however, his tune changed when the teen offered him an extra $10.
The purchase was made and the driver dropped the Year 11 students off at their party.
The spokesperson said it wasn't until her son came home, looking a bit worse for wear, and she asked how much he'd had to drink that she was told that the group had been bought a $20 box of Woodstock.
"At the time he thought it was genius as they all did, my son included, this is awesome but I was like 'what?!'"
Not only were the parents of the teens shocked by the behaviour, but the teen involved was also now feeling guilty.
"Now [the teen] is worried that he might have started something where the Uber driver thinks that it might be a quick way to double his fare ... that he might do it again. And now he's feeling really bad that he might have started something potentially quite dangerous and illegal, obviously."
She said Uber had "revolutionised" the lives of teenagers and their parents as it was seen as a trustworthy, cheaper option than getting a regular taxi. But now she's not so sure.
"Now it's just all of a sudden a false sense of security because while they're transporting them safely at the same time they're picking up booze on the way through and handing them basically a nuclear bomb to work with for the night.
"And that's the thing that really upsets me about it ... if this has happened, I suspect it's happened quite often."
In a statement, a spokesman for Uber said the "safety of its riders and driver-partners is a top priority".
"Our Community Guidelines set out the behaviour expected from both riders and drivers. People who breach these guidelines or our terms of service may be barred from using Uber, either temporarily or permanently depending on the seriousness of the breach."
A police spokesman said it was an offence to supply a minor, a person aged under 17, with alcohol.
"Police would take seriously any report of liquor being bought for minors. We would encourage anyone involved in such a scenario to make a report to police."
The offence can be met with a maximum fine of $2000.
Rebecca Williams, of Alcohol Healthwatch, said the incident should be referred to the police.
"He's broken the law. There is a law against supplying alcohol to young people ... it's clearly completely irresponsible, if that's what he's done."
However, she wasn't surprised and said it was typical of New Zealand's drinking culture.
"We can't be surprised that these things happen when we don't really address the broader context of it."
National MP Alastair Stewart, who is on Parliament's Transport Committee, said it wasn't just an issue about Uber but the fact people were buying young people alcohol.
"Just because he's working for Uber it doesn't make any difference, it's the same if it was any adult ... buying booze for a minor is not on. It's the same if a taxi driver did the same."
