Coupang is South Korea’s most popular online shopping platform, serving millions of customers with lightning-fast deliveries of products from groceries to gadgets.
Seoul has said the leak took place through overseas servers from June 24 to November 8.
But Coupang only became aware of it last month, according to police and local media, who said the company had issued a complaint in November against the alleged culprit – a former employee and a Chinese national.
On Tuesday, Lee ordered the government to “strengthen fines and make punitive damages a reality”, calling for “substantive and effective countermeasures”.
“The cause of the accident must be quickly identified and [those responsible] must be held strictly accountable,” he said.