Zynga is dealing with a patent infringement lawsuit from Agincourt Gaming for unspecified damages. This isn’t coming at the best of times, with Zynga preparing to file an iPO for an estimated $1 billion.

The lawsuit contends that all of Zynga’s major titles violate Agincourt’s patents, including Farmville, CityVille, FrontierVille, Zynga Poker, Empires & Allies, Mafia Wars, and Vampire Wars.

“Agincourt’s patents cover the most lucrative aspects of online social gaming,” said Bill Carmody, a senior partner at Susman Godfrey LLP, Agincourt’s lead counsel. “including those comprising the bulk of Zynga’s revenues—as they contain the crucial ‘link’ that allows for global, interactive prize redemption over the Internet.”

Zynga has had to deal with a number of trademark, copyright, patent, and IP issues in the past. Gene Quinn, president of IP Watchdog, calls Zynga’s patent portfolio “weak” adding that after the IPO, “Zynga will inevitably be the target of patent infringement litigation moving forward.”

Source: Inc.