Google said Monday it will enforce rules that require app developers distributing Android software on the Google Play Store to use its in-app payment system.

The move means that developers who have had customers pay them directly with a credit card for digital content will soon have to use Google’s billing system, which takes a 30 percent fee from payments, as reported in CNBC.

Up until now, it’s been Google’s policy for developers to use Google’s billing system on in-app purchases made within the Google Play store; however, it hadn’t been enforced, Google said in a blog post today.

It added that this policy is only applicable to less than 3 percent of developers with apps on Google Play.

“We only collect a service fee if the developer charges users to download their app or they sell in-app digital items, and we think that is fair. Not only does this approach allow us to continuously reinvest in the platform, this business model aligns our success directly with the success of developers,” Google said.

The clarification comes as a legal war heats up between Epic Games, creator of “Fortnite,” against Google and Apple. It erupted last month when the Cary-based games developer released a new payment system that skirts giving Apple and Google a 30 percent cut of the sales.

Epic Games is now offering the “Fornite Mega Drop” — a permanent 20 percent discount on V-Bucks, the in-game currency used in “Fortnite.” However, it only works if players paid Epic Games directly rather than using Apple or Google’s payment systems.

This broke rules applied by both stores.

Google and Apple subsequently banned “Fortnite” from its app stores.

“While Fortnite remains available on Android, we can no longer make it available on Play because it violates our policies,” Google said at the time.

Epic Games is now suing Google and Apple over the ban, while Apple has filed a countersuit.

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