Negotiators in the European Union have agreed to sweeping new rules that could change the very fabric of Apple’s iMessage service. In a press release Thursday night, the European Parliament announced that there is a provisional agreement between Parliament and Council negotiators on the Digital Markets Act that seeks to “ensure fair competition and more choice for users.”

During a close to 8-hour long trilogue (three-way talks between Parliament, Council and Commission), EU lawmakers agreed that the largest messaging services (such as WhatsApp, Facebook Messenger or iMessage) will have to open up and interoperate with smaller messaging platforms, if they so request. Users of small or big platforms would then be able to exchange messages, send files or make video calls across messaging apps, thus giving them more choice. As regards interoperability obligation for social networks, co-legislators agreed that such interoperability provisions will be assessed in the future.

While the rules haven’t become an official law, Apple would almost certainly be required to change iMessage’s closed nature. The law specifically takes aim at so-called “gatekeepers” that “provide certain services such as browsers, messengers or social media, which have at least 45 million monthly end-users in the EU.” Apple falls well within those parameters.

Apple’s iMessage platform has faced mounting public and regulatory pressure, but this rule would be a dramatic change for the platform, turning Messages into something of a universal messaging app. For example, if you choose to use iMessage, your messages would still be accessible in the WhatsApp app or some smaller messaging service on an Android phone and vice versa. It’s not entirely clear how this would affect innovation, privacy, or encryption, or even how it would be implemented, but it almost certainly wouldn’t be good.

The punishment for non-compliance is stiff. Companies that do not comply with the rules will receive a fine of up to 10 percent of their total worldwide turnover in the preceding financial year and 20 percent in the case of multiple infringements. If failure to comply becomes “systematic,” the company could be banned from acquiring other companies for an indeterminate period of time.

In a statement to The Verge, Apple said: “We remain concerned that some provisions of the DMA will create unnecessary privacy and security vulnerabilities for our users while others will prohibit us from charging for intellectual property in which we invest a great deal. We believe deeply in competition and in creating thriving competitive markets around the world, and we will continue to work with stakeholders throughout Europe in the hopes of mitigating these vulnerabilities.”

The rules are slated to go into effect six months after the rules are approved by both Parliament and Council.