Soverain Software, a Chicago-based patent-holding company that has been denounced on Capitol Hill, made tens of millions of dollars suing retailers with a patent on online shopping carts. That patent and two others were finally toppled when tech retailer Newegg won a key decision at the US Court of Appeals for the Federal Circuit in 2013. Soverain appealed that defeat all the way to the Supreme Court, but the company's legal pleas went nowhere.

Now Soverain is in what may be the final legal fight of its life—with its own lawyers. Soverain employed the law firm Jones Day, one of the nation's largest, from 2004 until 2010. At that point, the mega-firm decided to stop representing Soverain.

lawsuit (PDF) filed last month in Illinois state court shows that Soverain, which has no discernible business beyond filing patent lawsuits, continues to be in a serious dispute with its former law firm. In the lawsuit, Soverain claims that Jones Day's withdrawal "was wrongful and resulted in damages to Soverain, and also the parties disagreed on what amount of fees (if any) were due to Jones Day at the time of its withdrawal."

In 2011, Jones Day initiated an arbitration asking for fees, and Soverain filed a counter-claim. A hearing concluded on April 14, 2015, and it apparently didn't go Soverain's way.

A three-arbitrator panel awarded "substantial damages" to Jones Day, and Soverain is now seeking to throw out that award. The exact figures aren't known because both parties agreed to keep the information confidential, according to Soverain's lawsuit.

Whatever its amount, Soverain lawyers are asking for the award to be vacated. They say the panel disregarded the 2007 contract between the parties and implemented "its own notion of what would be reasonable and fair... without any semblance of contractual authorization."

The lawsuit contains little detail on what mistakes Soverain believes the panel of arbitrators made. "Soverain will seek the Court's guidance as to how to present its evidence while preserving such confidentiality to the fullest extent possible," the company says.

Neither Jones Day nor Soverain's attorneys responded to requests for comment on the case.