The world’s largest tech companies must comply with a sweeping new European law starting Friday that affects everything from social media moderation to targeted advertising and counterfeit goods in e-commerce — with possible ripple effects for the rest of the world.

One of the most comprehensive and ambitious attempts by policymakers anywhere to regulate tech giants through legislation will be the EU’s unprecedented measures for online platforms, which will apply to companies such as Amazon, Apple, Google, Meta, Microsoft, Snapchat and TikTok, among many others. Fines could be imposed on some companies and changes in software could affect consumers.

The rules seek to address some of the most serious concerns that critics of large tech platforms have raised in recent years, including the spread of misinformation and disinformation; possible harms to mental health, especially for young people; rabbit holes of algorithmically recommended content and lack of transparency; and the spread of illegal or fake goods on virtual marketplaces.

Although the EU’s Digital Services Act (DSA) passed last year, companies have had until now to prepare for its enforcement. A key compliance deadline approaches Friday – after which tech platforms with more than 45 million EU users must meet the law’s requirements.

According to the EU, the law aims to “create a level playing field to foster innovation, growth, and competitiveness on both the European Single Market and the global market.” This reinforces Europe’s position as a leader in checking the power of big US tech companies.

For all platforms, not just the largest, the DSA bans data-driven targeted advertising aimed at children, as well as targeted advertising based on protected characteristics such as political affiliation, sexual orientation, and ethnicity. The restrictions apply to all kinds of online ads, including commercial advertising, political advertising and issue advertising.