"With face coverings now being mandatory while you travel on public transport we wanted to make it easy for our customers to buy a mask before they started their journey.
"We were particularly targeting anyone who had left their mask at home. We worked with our partners Office Max and Sanitarium to develop a product that would work in the machines."
While the move has been backed by a number of people online, some weren't happy with the price.
Freebairn says they believe $9 for a pack of four is an affordable price and covers the cost of stocking and servicing of the machines.
"We are selling four masks for $9. We came up with that price based on the cost of the stock, a contribution towards reconfiguring the vending machines and on-going servicing by Sanitarium.
"We were very conscious that the masks needed to be an affordable option for customers.
"The first stock went in last week and we have already sold 45 packs of four."
Auckland Transport's move comes after the Government made it mandatory for people in Auckland to wear face masks on public transport as well as on domestic flights.
The new rules are "another line of defence" when it comes to the country's Covid-19 response plan, Ardern told reporters last month.
"Now is the right time to make mask use mandatory in these situations. It will provide another line of defence, is a low-cost and practical option and presents a minor inconvenience by comparison."
Previously, the mandatory use of masks on public transport was reserved for level 2 and above.
The rules can be enforced by police, according to Covid-19 Response Minister Chris Hipkins, but the focus would be to "educate and encourage".
By law, people can be punished if they don't follow the new rules but Hipkins said this would be a "last resort".
Both Prime Minister Jacinda Ardern and Hipkins were at pains to point out that it will not be up to bus drivers to enforce the rules.
"We're not expecting bus drivers to stop the bus and enforce these measures," Hipkins said.
Children and young people travelling to and from school are exempt from face-covering requirements on school buses and other school transport.