Facebook parent Meta will only be able to run advertising based on personal data with users' consent, according to a confidential EU privacy watchdog decision, a person familiar with the matter said, in a blow to the social network.

The Irish data protection agency, which oversees Meta because its European headquarters is located in Dublin, has been given a month to issue a ruling based on the European Data Protection Board's (EDPB) binding decision.

The EDPB will likely require the Irish body to hand out fines, the person said, asking not to be named because of the sensitivity of the issue.

Big tech's targeted ad model and how data is collected and used has drawn regulatory scrutiny around the world.

The Irish case against Meta was triggered by a complaint by Austrian privacy activist Max Schrems in 2018.

"Instead of having a yes/no option for personalised ads, they just moved the consent clause in the terms and conditions. This is not just unfair but clearly illegal. We are not aware of any other company that has tried to ignore the GDPR in such an arrogant way," Mr Schrems said in a statement.