The patent battle between Motorola and Microsoft heated up once again on Tuesday.

An administrative law judge for the U.S. International Trade Commission ruled on Tuesday that Motorola has infringed on one of Microsoft’s patents. The patent in question covers meeting scheduling and appointments from mobile devices. The patent was originally filed in 2002 and forms part of seven patents at the heart of Microsoft’s complaint against Motorola. The software giant accused Motorola Mobility of infringing seven patents that the company holds. Microsoft asked the ITC to block imports of some Motorola Android phones in the United States as part of the complaint.

“We are pleased with the ITC’s initial determination finding Motorola violated four claims of a Microsoft patent,” said David Howard, Microsoft corporate vice president and deputy general counsel. “As Samsung, HTC, Acer and other companies have recognized, respecting others’ intellectual property through licensing is the right path forward.”

Microsoft’s claims center around mobile phone patents which is slowly becoming the battle ground for Google, Apple and Microsoft. Google announced earlier this year that it plans to acquire Motorola Mobility for $12.5 billion. Google CEO Larry Page noted at the time of the deal announcement that Microsoft and Apple are “banding together in anti-competitive patent attacks on Android.” Citing recent patent auctions, Page expects that Google’s acquisition will help protect Android in the future. A number of analysts believe Google’s deal could be beneficial to Microsoft’s Windows Phone, creating more competition between the three major smartphone operating systems.

Motorola responded to the ruling on Tuesday by welcoming clarity on the definition of Microsoft’s patent. ”We are very pleased that the majority of the rulings were favorable to Motorola Mobility,” said Scott Offer, senior vice president and general counsel of Motorola Mobility.  “The ALJ’s initial determination may provide clarity on the definition of the Microsoft 566 patent for which a violation was found and will help us avoid infringement of this patent in the U.S. market.”

Microsoft claims the ruling will affect 18 of Motorola’s products. Horacio Gutiérrez, Microsoft’s corporate vice president and deputy general counsel, revealed the figure in a Twitter message on Tuesday. “At least 18 Motorola products impacted by ITC’s finding of patent infringement by Motorola, including the Atrix, Droid and Xoom tablet,” said Gutiérrez.