South Korea's Personal Information and Protection Commission said it fined Google 69.2 billion won and Meta 30.8 billion won after a meeting where officials agreed that the companies' business practices might cause serious" privacy infringements.
The fines were the biggest ever penalties imposed by South Korea for privacy law violations, the commission said in a press release.
Both companies refuted the commission's findings and Meta indicated it could challenge the fine in court.
The fines can be appealed through administrative lawsuits, which must be filed within 90 days after the companies are formally notified of the commission's decision.
According to the commission, Google and Meta, which operates Facebook and Instagram, didn't clearly inform users or obtain their consent as they collected information about their online activities when they used other websites or services outside their own platforms.
Such data was used to analyse their interests and create individually customised advertisements, the commission said.
The commission ordered the companies to provide an "easy and clear" process of consent giving people more control over whether to share information about what they do online.
"Google did not clearly inform consumers that it would collect and use their behavioural information about their use of other companies' (services) when they signed up," the commission said.
"Meta did not present the content of consent in way that could be easily seen by consumers when they signed up, and just included the content in their full data policy statement. It did not specifically inform consumers of the legally required notifications and did not obtain their consent."
The commission said the companies' practices seriously threatened privacy rights as more than 82 per cent of South Koreans using Google and more than 98 per cent using Meta have let the companies track their online activities.
Google, a search and email giant that also operates the YouTube video platform, disagreed with the commission's findings.
It said in a statement that it has always demonstrated a commitment to "making ongoing updates that give users control and transparency." The company said it will review the commission's findings once it receives the fully written decision.
Meta said it will consider "all options," including seeking a ruling from court.
"We are confident that we work with our clients in a legally compliant way that meets the processes required by local regulations," Meta said in an emailed statement.
