Digital Lifestyle Outfitters parent company Netalog has filed a patent infringement lawsuit against Belkin.
The suit makes similar claims to those the company is making in a separate case against Griffin Technology.
DLO alleges that Belkin's TuneBase FM product infringes Netalog's patent on an "FM Transmitter and Power Supply/Charging Assembly for MP3 Player." Netalog wants damages.
It filed a similar suit against Griffin in September 2004, this time over alleged patent abuse in Griffin's RoadTrip.
Both Griffin and Belkin dismiss the claims.
Griffin said: "We do not believe that the DLO patent is valid, nor that any of our products infringes the patent. In 2004 we sued Netalog for a declaration to that effect; that their patent is invalid and not infringed upon," the company said, and has asked for the suit to be dismissed.
Belkin general counsel Chris Flower told MacMinute: "It is Belkin's firm belief that such complaint has no merit and Belkin has specified a number of defenses to the Complaint, including but not limited to invalidity of the patent."
Belkin has made countersuits against Netalog and Flower is "confident" the suit will be settled in Belkin's favour.