Back in July, I blogged about how the co-founders of the VoIP service Skype, Niklas Zennstrom and Janus Friis, accused eBay of violating its licensing agreement regarding Skype’s underlying technology. To sum up: the co-founders sold the company called Skype to eBay but retained the copyright on the technology that Skype uses to function. While eBay owns Skype, it has to license the technology from the co-founders. Zennstrom and Friis say that eBay has violated the terms of that license and have pursued legal action in British courts.

Now the New York Times reports that the co-founders have expanded the battle to the United States. Yesterday, Zennstrom and Friis filed a copyright infringement lawsuit in the District Court of Northern California.

I imagine the Skype team at eBay has a large supply of antacids on hand right now. Since day one of eBay’s acquisition of Skype, tech journalists have questioned the purchase. Originally, eBay had hoped to incorporate Skype’s technology in its auction process. Ideally, potential customers could talk with people offering up items for sale. But eBay never found a way to integrate Skype into its architecture.

Now eBay is attempting to sell off a significant percentage of ownership of Skype to a group of private investors. But it turns out that people looking to buy a company usually don’t like to complete a purchase in the middle of legal issues. A lawsuit could complicate matters and put the sale on hold indefinitely.