(CNN) -- Facebook games will have to reveal any in-app charges and will no longer be allowed to give players bonuses for "liking" their pages under new rules rolled out for developers this week.
So-called "freemium" games and other apps have become a popular choice for developers using Facebook or other platforms, like Apple's iOS and Google's Android mobile operating systems.
Instead of paying for an app up front, players may download a game for free. In most cases, they can then play a basic version of that game, but get access to new content or in-game items that help their progress by paying.
In addition to being arguably deceptive, this approach also has brought attention through several cases in which children have unknowingly racked up thousands of dollars worth of charges by making purchases in games that their parents didn't realize allowed that option.
"If your game includes mandatory or optional in-app charges, explain this in your app's description," Facebook's new rule reads.
The curb on encouraging "likes" appears to be an effort by Facebook to keep developers from artificially inflating the popularity of their games.
On Facebook, a page's popularity is judged, in part, by the number of likes, posts, comments and shares it gets. More popular pages rank higher in the site's search results and are shown to more users.
It's not uncommon for games to offer players extra in-game items for liking their page.
But intentionally pumping up a page's popularity is a problem Facebook has been working to control. In the worst case scenario, "like farming" is being done by someone who shares content with no other purpose than to make it go viral.
Once the page has gotten lots of likes, the owner can strip it down and change it to a page promoting a product or service or even sell it to someone else on black-market sites.
Facebook has worked to crack down on that practice with tools including one that devalues any post that specifically asks users to like or share it.