Big Tech goes from 'teenager' to 'grown-up' under landmark EU law. Here's what you need to know

An EU law that seeks to rein in large digital companies has officially kicked in, spelling big changes for primarily U.S. tech giants.

The European Union's landmark Digital Markets Act officially became enforceable on Thursday. That means the European Commission, the EU executive arm, can start taking action against companies that breach the rules.

The Digital Markets Act aims to clamp down on anti-competitive practices from tech players, as well as force them to open out some of their services to other competitors. Smaller internet firms and other businesses have complained about being hurt by the practices of these companies.

Bill Echikson, a non-resident senior follow at the Center for European Policy Analysis (CEPA), said that the EU reforms mean that technology giants will graduate from "teenagers" to "grown-ups" now.

"There's a lot of changes that could or could not happen. A lot of it is uncertain," Echikson said. But, he added, the new law could inspire change in other countries, like the U.S. and the U.K. and ultimately force tech firms into global tweaks to their platforms.

CNBC runs through how the law impacts large U.S. tech companies — as well as consumers in the EU.

The EU Digital Markets Act primarily impacts U.S. tech giants — the likes of Alphabet, Amazon, Apple, and Meta.

That's because the rules impose strict curbs for so-called "gatekeepers" — firms with an entrenched position in their respective market, with a market capitalization of at least 75 billion euros ($81.7 billion) and with a platform with 45 million monthly active end users in the EU.

That makes U.S. tech giants a key target. So far, six firms have been designated gatekeepers: Alphabet, Amazon, Apple, Meta, Microsoft and China's ByteDance — the