Apple has changed the rules around how games on its app store use loot boxes.
These boxes are random rewards for gameplay and often give players benefits and power-ups that can be used in games.
In a change to its developer guidelines, Apple said games must now let players know the odds of getting particular items in the boxes.
Loot boxes have been controversial for some time with some experts saying they amount to a covert lottery.
In the updated guidelines, Apple said any in-game mechanism that rewards players with "randomised virtual items" must list the odds of receiving each type of item. In addition, it said, customers must be informed of these odds before they buy the boxes or rewards.
Many games offer extras to players that can change the appearance of the game, introduce new characters or bestow power-ups that help people as they play.
Some titles let people buy loot boxes with in-game funds they generate by playing or by spending real money to purchase the game's virtual cash.
The controversy over the crates was thrown into sharp focus last month with the release of the Star Wars Battlefront II game, which used them extensively.
US politicians called for greater regulation of games that use loot boxes and crates. One politician said Battlefront II was a "Star Wars-themed online casino".
The backlash led Electronic Arts, the publisher of the Battlefront II, to re-work it to remove its reliance on the random reward system.
In the UK there have been calls for games that use the loot systems to be regulated like other lotteries.
The UK's Gambling Commission said the boxes did not come under its control because the rewards they handed out were only usable in the game.