BRUSSELS, Feb 6 (Reuters) - Social media app TikTok was charged by EU tech regulators on Friday with breaching EU online content rules through its addictive features and was told that it may have to change the design of its app or risk a fine of as much as 6% of owner ByteDance's global turnover.

The European Commission set out its charges in preliminary findings to TikTok following a year-long investigation under the Digital Services Act (DSA) which requires large online platforms to do more to tackle illegal and harmful content.

TikTok criticised the charges.

"The Commission's preliminary findings present a categorically false and entirely meritless depiction of our platform, and we will take whatever steps are necessary to challenge these findings through every means available to us," a TikTok spokesperson said.

The EU charges focused on TikTok's addictive design which includes features such as infinite scroll, autoplay, push notifications, and its highly personalised recommender system.

The Commission, which acts as the EU tech enforcer, cited the platform's generation of new content to constantly reward users which fuel the urge to keep scrolling and shift users' brain into autopilot mode as an example of an addictive feature.

The EU regulator said TikTok did not adequately assess how these addictive features could harm the physical and mental wellbeing of its users, including children and vulnerable adults.

It accused TikTok of disregarding important indicators of compulsive use of the app, such as the time that minors spend on the app at night and the frequency with which users open the app.

The EU watchdog said TikTok seems to fail to implement reasonable, proportionate and effective measures such as screentime management tools and parental control tools to mitigate risks due to its addictive design and that the company needs to change the basic design of its service.

"So now we are expecting after that, when we are publishing these preliminary findings, that Tiktok has to take actions and they have to change the design of their service in Europe to protect our miners," EU tech chief Henna Virkkunen told reporters.

She said investigations into other online platforms were advancing well and that decisions are expected in the next weeks and months, without naming any company.

TikTok can ask to see the Commission's documents and provide a written response before the watchdog issues a decision.

The company last year settled charges of infringing a DSA requirement to publish an advertisement repository allowing researchers and users to detect scam advertisements.