That meant, Ardern said, answering Hosking's probing on whether it was a new tax, that it was not.
"No one would argue GST was a new tax," the Prime Minister said.
The extension would provide the fairness that New Zealand retailers had been asking for, she said.
Before the last election, Labour promised not to implement tax changes this term arising from the tax working group.
But applying GST to low-value goods was specifically ring-fenced from that promise by Labour's revenue spokesman at the time, Michael Wood.
The process was already being developed in the system by IRD under the National-led Government.
GST is payable on all goods bought in New Zealand, including online purchases such as books bought on Amazon or Book Depository or goods from Alibaba and e-Bay.
But the cost of collecting it on small items such as a $40 book means it is not collected.
Today's announcement is likely to find a way to make large sellers comply with New Zealand law by registering and collecting GST.
While the tax will be paid by the foreign firms selling the goods the cost would inevitably be passed on to the buyer in the form of increased prices.