Meta must change Facebook's and Instagram's "addictive" design or face a heavy fine, the EU has warned.
In its preliminary findings, the European Commission said features such as infinite scroll, autoplaying videos and personalised recommendations could encourage "compulsive use", particularly among children and teens.
If Meta does not make suitable changes, it could be fined up to 6% of its total global annual turnover.
A spokesperson for the tech giant told the BBC it disagreed with the findings "which don't accurately take into account the significant steps we've taken to protect teens".
In the preliminary findings, the Commission said the endless stream of content "shift the brain into autopilot mode, contributing to unhealthy habits".
In particular, it is particularly concerned about the impact social media platforms may have on younger users.
"Protecting the physical and mental health of Europeans must be a priority for social media platforms," EU tech chief Henna Virkkunen said in a statement.
The Commission said Meta failed to adequately assess the risks posed by how Facebook and Instagram were designed, as well as how long children spend on the platforms, particularly at night.
It raised concerns about features such as Reels and Stories, arguing they could contribute to excessive use, and claimed Meta's safeguards do not go far enough.
The Commission said time-management tools on Facebook and Instagram, including those enabled by default for teenagers, can be dismissed and do not meaningfully reduce usage.
And it also criticised Meta's parental controls, arguing they are only effective if parents have the time and technical expertise to understand and use them properly.
But Meta said it had rolled out Teen Accounts that "automatically protect teens and put parents in control - allowing them to block access to Instagram at night and cap daily screen time at just 15 minutes".
