The list -- on which services from Amazon, Google, Meta, Instagram and Microsoft also feature -- all have more than 45 million monthly active users.
That puts them in a category under a new EU law, known as the Digital Services Act (DSA), imposing measures from August such as annual audits and a duty to effectively counter disinformation and hate content.
In four months' time, "these platforms and search engines will not be able to act as if they were 'too big to care'," Thierry Breton, the EU's internal market commissioner, said in a statement.
"This new supervision system will cast a wide and tight net and catch all points of failure in a platform's compliance," he added.
Platforms meeting the 45-million-plus threshold include Twitter, owned by US billionaire Elon Musk; Alphabet's Google Search, Google Maps, Google Shopping and Google Play units as well as its YouTube subsidiary; and Meta's Facebook and Instagram.
Others are Microsoft's LinkedIn, Apple's iOS App Store, online encyclopedia Wikipedia, messaging app Snapchat and creative image website Pinterest.
Under the DSA, they are categorised as a "Very Large Online Platform" (VLOP) or a "Very Large Online Search Engine" (VLOSE).
Most of the companies on the list are US-based, but Chinese-owned platforms TikTok and e-commerce site AliExpress also feature.
The commission also listed German online fashion retailer Zalando.
- Huge fines -
Breton told journalists on Tuesday his team will hold "stress tests" to check Twitter's compliance readiness "at the end of June".
He added that TikTok had also expressed an interest in cooperating to ensure compliance.
Tuesday's announcement follows a deadline in February for online companies to publish user figures in Europe.
The DSA has a wide range of objectives, including forcing platforms to better protect children, strengthen transparency around digital services, prohibit the sale online of unsafe goods and allow users to have greater choice when online in the EU.
The rules allow the EU to impose fines of up to six percent of the platforms' annual global sales for repeated infringements.
By August 25, 2023 the 19 platforms must have an independent compliance system in place and give their first annual risk assessment to the European Commission, including how they plan to handle content on mental health and gender-based violence.
There will then be an independent audit and oversight by the commission.
Commission vice president Margrethe Vestager said the designations were a "huge step forward" for the DSA to bring "meaningful transparency and accountability of platforms and search engines and give consumers more control".
Online platforms declaring themselves below the 45-million user threshold include Swedish music-streaming site Spotify, US dating app Tinder and home-rental platform Airbnb.
Breton said "four to five" more platforms could be added to the list "in the coming weeks" but refused to name which ones.
The DSA is one of two major laws the EU passed last year to rein in digital platforms to protect EU users.
The special obligations for very large platforms are in addition to the DSA rules that will apply to all from February 17, 2024.
The second law, the Digital Markets Act, prohibits anti-competitive behaviour by so-called "gatekeepers" of the internet.
raz/rmb/giv
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