European Commission on Wednesday said it designated six tech giants as “gatekeepers” under its new Digital Markets Act — a strict set of rules that could shake up the business models of large digital platforms.

Amazon, Alphabet, Apple, Microsoft, Meta and ByteDance will have six months to bring their core platform services into compliance with the obligations laid out in the EU’s DMA, the Commission said.

The Commission said that Amazon, Apple, Alphabet, Meta, Microsoft and China’s ByteDance are deemed as “gatekeepers.” The term refers to massive internet platforms that the EU views as restricting access to core platform services, such as online search, advertising, messaging and communications.

In addition, five new market investigations were opened into U.S. tech giants Microsoft and Apple, evaluating whether some of their services should be considered gatekeepers.

The EU will study submissions from Microsoft and Apple as part of these probes. As gatekeepers, Microsoft’s Bing, Edge, and Microsoft Advertising platforms and Apple’s iMessage service meet the EU’s criteria. The opposite is argued by Microsoft and Apple.

As part of its investigation, the EU will also examine whether Apple’s iPadOS operating system, which powers Apple’s iPad tablets, should be pronounced a gatekeeper, despite the European Commission’s claims.

The Digital Markets Act is a ground-breaking new EU law aimed at combating anticompetitive practices by big tech companies. Several internet companies and other businesses have complained that these companies’ business practices hurt them.

The mobile operating systems of Google and Apple, which are the two major OS platforms worldwide, charge a 30% fee for in-app purchases, which Spotify and Epic Games claim is too high.

The Digital Markets Act poses privacy and data security risks for Apple’s users, the company said. According to Apple, the DMA could weaken security for its iMessage platform – the EU wants Apple to make it easier for iMessage to work with rival messaging apps like WhatsApp.

Apple’s spokesperson told CNBC on Wednesday that the company will focus on mitigating these impacts and continuing to provide its European customers with the best products and services. 

Additionally, the EU designated Chinese firm Byte Dance as a gatekeeper. TikTok, the company’s social media platform, has come under greater scrutiny globally, with regulators concerned about its growing popularity and the potential for spreading disinformation.