Lodsys, well known for targeting several independent iOS app developers with patent infringement lawsuits, is finding itself on the defensive end of a legal filing alleging the patents it holds aren’t valid. The claim was filed by ForeSee Results in U.S. District Court in Northern Illinois on behalf of several of its clients.

ForeSee Results filed a proactive declaratory judgement action on Tuesday  against all four of the patents Lodsys holds after the the patent holder threatened legal action against its clients, according to Foss Patents. Clients ForeSee Results claimed were threatened included Adidas, Bust Buy and WE Energies.

Lodsys is also facing patent invalidation filings from Brother, Canon, HP, Hulu, Lenovo, Lexmark, Motorola Mobility, Samsung, and Trend Micro. The filings came in response patent infringement lawsuits against the companies over their printer products.

Lodsys is currently targeting seven different companies that develop apps for the iPhone, iPad, iPod touch, OS X and Android with claims that the in-app purchase and upgrade system they use needs to be licensed individually even though Apple and Google already have patent deals in place.

Apple’s legal team sent a letter to Lodsys’s CEO, Mark Small, explaining that his interpretation of their license agreement was wrong, and that independent developers are covered under under the deal. Lodsys, however, seems certain that it’s on solid ground with the lawsuits.

“Unfortunately for Developers, Apple’s claim of infallibility has no discernable basis in law or fact,” the company said. “Lodsys has carefully considered this issue and consulted several legal experts to consider Apple’s claims. We stand firm and restate our previous position that it is the 3rd party Developers that are responsible for the infringement of Lodsys’ patents and they are responsible for securing the rights for their applications.”

Should ForeSee Results convince a judge to declare the Lodsys patents invalid, iOS app developers could use the ruling to their advantage should the lawsuits against them move forward. Since the developers may be on their own for mounting a defense — and shouldering the legal fees — they may find they have to cave in to Lodsys’s demands if the court in Illinois doesn’t move quickly with a ruling.

Lodsys hasn’t commented on the ForeSee Results filing.