Google has always required apps offered on the Play Store's virtual shelves to use its payment system, which takes an industry-standard 30 percent commission, but has been lax about enforcing the rule

Google said Monday it plans to start enforcing a rule requiring Android apps in its Play store to use its payment system, which takes a 30 percent cut of transactions.

"We have clarified the language in our Payments Policy to be more explicit that all developers selling digital goods in their apps are required to use Google Play's billing system," product management vice president Sameer Samat said in a blog post.

People with smartphones or tablets powered by Google-backed Android software are free to get apps from online venues other than the Play Store run by the internet giant.

Google has always required apps offered on the Play Store's virtual shelves to use its payment system, which takes an industry-standard 30 percent commission—the same as Apple does in its App Store for iOS-powered .

Unlike Apple, however, Google has been lax about enforcing the rule.

Google said the policy applies to fewer than 3 percent of developers with apps in the Play Store.

"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," Samat said.

Changes coming to the next version of Android, due out next year, will make it easier for people to use other app stores while watching out for user safety, according to Samat.

"Even if a developer and Google do not agree on business terms the developer can still distribute on the Android platform," Samat said.

"This is why Fortnite, for example, is available directly from Epic's store or from other app stores including Samsung's Galaxy App store."

Apple and Google in August pulled video game sensation Fortnite from their mobile app shops after its maker, Epic Games, released an update that dodges revenue-sharing with the tech titans.

The latest version of Fortnite contains a that lets player transactions bypass Apple's App Store and Google's Play, preventing the firms from collecting their typical cut.

Epic quickly filed a federal lawsuit against Apple, accusing the iPhone maker of wielding monopoly power.

The suit said Epic is not seeking favorable treatment, but is asking the court to order Apple to change its commission structure for all developers.

Apple said Fortnite was pulled after "Epic Games took the unfortunate step of violating the App Store guidelines that are applied equally to every developer and designed to keep the store safe for our users."