FARMVILLE, Cafe World, Mafia Wars, Petville - Facebook could be on the verge of losing a key part of what makes it so popular.

Zynga - the company behind four of Facebook's top 10 social gaming apps - has had enough of the site's increasing love of cash, according to Techcrunch.

Following an escalating battle over Facebook credits, Zynga has begun preparing its own social gaming network, Zynga Live.

Facebook Credits is the only payment platform the site will allow its app developers to use. Facebook takes a 30 per cent cut of any revenue generated through Facebook Credits.

A Zynga source told Techcrunch that CEO Mark Pincus confirmed the move last Thursday in a staff meeting and Facebook isn't taking the news well.

Several weeks ago, Facebook shut down third-party notifications for some of Zynga's games - including Farmville - which has seen its app drop some 10 million users as a result.

Farmville, which at its peak was played by 80 million Facebook users, has lost four million of them since mid-April.

If the split happens, Farmville will form the basis of Zynga's first independent site, Farmville.com, given that Facebook is also threatening to remove Zynga's games altogether.

The notification crackdown has not just cut into Zynga's audience.

MindJolt Games lost a third of its 21 million player user base, while Facebook's second-most popular game, Birthday Cards, suffered a 5.5 million drop, according to GamePro.

Industry insiders are following the rise in tension, and most agree that Facebook can live without Zynga, but Zynga can't live without Facebook.

Businessweek claims it will generate more than $500m in 2010 and has quarupled its staff to 775 in the past 12 months.

Last week, it notified the share market of plans to issue shares that would value the company at more than $4 billion, so Zynga will not make any decision to break with Facebook lightly.

But discussions are at a critical level - today, games.com published a domain registration form that confirms the existence of zyngalive.com.