The European Union has formally announced it suspects X, previously known as Twitter, of breaching its rules in areas including countering illegal content and disinformation.
Digital commissioner Thierry Breton set out the alleged infringements in a post on the social media platform.
He said X, which is owned by Elon Musk, was also suspected of breaching its obligations on transparency.
X said it was “co-operating with the regulatory process”.
In a statement the firm said it was “important that this process remains free of political influence and follows the law”.
“X is focused on creating a safe and inclusive environment for all users on our platform, while protecting freedom of expression, and we will continue to work tirelessly towards this goal,” it added.
In October the EU said it was investigating X over the possible spread of terrorist and violent content, and hate speech, after Hamas’ attack on Israel.
X said then that it had removed hundreds of Hamas-affiliated accounts from the platform.
The investigation was the first under the EU’s new tech rules.
Under a piece of legislation introduced in August, the Digital Services Act (DSA), big tech firms operating in the EU have beefed up obligations to protect users.
Breaches can result in huge fines or services being suspended.