Google Inc. has been on a losing streak in its fight to keep customer data stored on overseas servers out of reach from U.S. law enforcement authorities.

Last week, a federal magistrate judge in San Francisco denied Google's attempt to quash a warrant seeking data stored abroad. It was at least the third such decision involving Google in as many months, and another magistrate judge in Florida in early April forced Yahoo to hand over data in a similar ruling.

The momentum in favor of law enforcement raises questions about whether a landmark decision last year by the U.S. Court of Appeals for the Second Circuit curtailing authorities' power to access overseas data is in danger of being upset. But it also spotlights the particular challenges faced by Google's approach in waging these courtroom battles.