About 310,000 Australian Facebook users are set to find out their personal information may have been accessed by Cambridge Analytica.
The social media behemoth is expected from Monday afternoon to notify the 87 million users worldwide whose data may have been unknowingly and "improperly" shared with the British political consulting agency.
About one in 50 Australian users and one in every three American users are among those affected.
Cambridge Analytica developed controversial tools for use in political campaigns and worked on Donald Trump's run for US president.
It says it received data on 30 million users but never used that information in the 2016 campaign.
The Mark Zuckerberg-led social media giant will also show each of its 2.2 billion users a message prompting them to review the apps and websites connected to their account.
The Privacy Commissioner is investigating whether Facebook breached the Privacy Act, which requires organisations meet certain obligations including taking reasonable steps to ensure personal information is held securely.
Facebook has lost $100 billion of its sharemarket value since the Cambridge Analytica scandal broke three weeks ago.
It last week suspended another political consulting firm amid media reports it had ties to Cambridge Analytica and received more than $4.5 million during Brexit from the triumphant Vote Leave campaign
The Canadian-based AggregateIQ says it has never been part of Cambridge Analytica or parent company SCL and has never entered into a contract with Cambridge Analytica.
