Motorola sued over patents used in Android phones
Motorola is being sued in a patent row by a company partly bankrolled by Google - which wants to buy Motorola.
Intellectual Ventures is taking legal action over six patents, all of which are used in Android smartphones produced by Motorola.
The lawsuit has been filed, said Intellectual Ventures, after talks over a licensing deal broke down.
Patent experts said the case was "concerning" and cast doubt on Google's ability to defend Android partners.
Intellectual Ventures, set up by Microsoft's former chief technology officer Nathan Myhrvold, has built up much of its pool of about 35,000 patents by buying intellectual property from inventors. It then generates money for investors by signing licensing deals with hi-tech firms that use the patented technologies.
The company has accused Motorola Mobility of using its technology to perform file transfers, updates and remote data management and other functions on some of its smartphones.
In a statement, Intellectual Ventures said it had been in discussion with Motorola since January 2011 but the talks had failed to produce an agreement.
"We have a responsibility to our current customers and our investors to defend our intellectual property rights against companies such as Motorola Mobility who use them without a license," it said. It is now seeking a trial and unspecified damages.
Ironically, a separate licensing deal negotiated in late 2010 revealed that Google was one of dozens of firms that put cash into Intellectual Ventures' investment funds.
This is not the same fund that is being used to take legal action against Motorola, but one expert said the case raised questions about Google's ability to help its partners.
Patent expert Florian Mueller said Google's backing of Intellectual Ventures was an "own goal" and said that its failure to defend Android partners was "inexcusable".
This failure was particularly acute in the case of Motorola Mobility, he said, as in mid-August Google put down a $12.5bn (£8bn) bid to acquire it.
Neither Motorola Mobility nor Google has commented on the case.