New Facebook rules which prevent apps from sending notifications to users have caused the number of people playing Facebook games to drop sharply.
According to a report by Gamasutra, Zynga's FarmVille has lost more than 4.4 million monthly players in the four weeks following the notifications tweak.
And out of the top 25 social games on Facebook for April, 18 saw player numbers decline, with 12 of those relinquishing at least a million users.
MindJolt Games - a portal for more than a 1000 casual titles - suffered the biggest losses, ending April with nearly eight million fewer monthly users, down from over 20 million in March.
Facebook announced the move to stop applications from sending notifications last October, citing the reason for the move as an attempt to simplify Facebook.
"When we launched Facebook Platform in 2007 there were just 40 million users on Facebook. Since then, in less than three years, more than 350 million users have joined Facebook, and more than one million developers like you have created more than 500,000 applications," the company confirmed to developers on its developer blog.
"With this additional scale came greater complexity. We announced last October a set of efforts to help make interactions with applications more streamlined, clear, and less spammy for users."
FarmVille monthly users dropped from 82.8 million users to 78.4 million throughout April, while other big losers included CrowdStar's Happy Aquarium, which dropped 4.2 million to 19.5 million.
Hi5 president and CEO Alex St John criticised Facebook's U-turn on its app policies at GDC earlier this year saying that the platform had an identity crisis.
"Zynga took off and suddenly their users are being spammed with game invitations and Facebook's going, 'whoa, that's huge and, oh my god our customers are complaining, what do we do?'" he said, adding that the result has been "schizophrenia" in how the platform promotes its content.