Both organisations develop tools that allow hobbyists to control and manage model railways using computers.
KAM Industries alleges that the open source project, which is run by Robert Jacobson, violates a patent owned by KAM.
The firm has not filed any legal claims, but has invoiced Jacobson $29 per distributed copy of its application, a total of $203,000.
Jacobson has retaliated with a lawsuit against KAM Industries and its founder Matthew Katzer.
The suit asks the court to invalidate the patent and rule that the company engaged in illegal acts to monopolise the market for multi-train control software in the US. He is also demanding $50,000 in damages as well as punitive damages.
The case offers a rare example of a patent holder going after an open source developer, which is generally believed to be the Achilles heel of open source projects.
There have allegedly been previous cases, but these have been settled by the defendant agreeing to a non-disclosure clause thereby keeping the details under wraps.
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