Countdown spokesman James Walker said the company was "extremely disappointed" to have failed the controlled purchase operation in Grey Lynn last year.
"We do 2.7 million customer transactions every week and this time we made a mistake."
Mr Walker said Countdown wanted to apologise to our customers for the inconvenience the five day suspension may cause and said a full review of the company's alcohol sale policy and the way we train our staff had been conducted.
An online training module for staff had been introduced, as well as independent training of all managers and supervisors by LCQ qualified instructors this year.
Additionally, store managers would now assess supervisors monthly on the way they conduct alcohol transactions, he said.
Williamson Ave will join 18 other Countdown stores who have had their liquor licences suspended for alcohol-sale breaches in the last four years.
In September last year, three Auckland supermarkets - in Sylvia Park, St Johns and Mt Roskill - were banned from selling booze for between three and five days.
The store's managers also had their licences suspended for 30 days.
In January 2015 Takapuna Countdown lost an appeal against a ruling to suspend their licence for a week after selling beer to a man so drunk he could barely stand.
The store battled the penalty for nearly a year after the Alcohol Regulatory and Licensing Authority imposed the suspension.
In addition, since June 2011, the sale of alcohol has been suspended in Countdown supermarkets in Onehunga, Whangarei, Waiheke, Taupo, Takapuna, Ashburton, Nelson, Hastings, Nelson, Te Awamutu, Wainuiomata, Mosgiel, Hamilton, Dunedin and Paraparaumu.
First Union national organiser Tali Williams said the breaches of liquor laws at Countdown stores were linked to staffing levels.
"If there are insufficient staff on at checkouts, mistakes will be made by rushed supervisors and checkout staff.
We are pleased to note that Countdown has committed to introducing increased staffing hours, particularly in the checkouts, and we are hopeful this will deal with the problem of liquor law breaches."
The problem was widespread among supermarket chains, she said. "This is not just Countdown, New World and Foodstuffs also have similar problems."