Microsoft is suing the US government for the right to tell its customers when a federal agency is looking at their emails, the latest in a series of clashes over privacy between the technology industry and Washington.
The lawsuit, filed in federal court in the Western District of Washington, argues that the government is violating the US Constitution by preventing Microsoft from notifying thousands of customers about government requests for their emails and other documents.
The government's actions contravene the Fourth Amendment, which establishes the right for people and businesses to know if the government searches or seizes their property, the suit argues, and the First Amendment right to free speech.
Microsoft's suit focuses on the storage of data on remote servers, rather than locally on people's computers, which Microsoft says has provided a new opening for the government to access electronic data.
Using the Electronic Communications Privacy Act, the government is increasingly directing investigations at the parties that store data in the so-called cloud, Microsoft says.
The 30-year-old law has long drawn scrutiny from technology companies and privacy advocates who say it was written before the rise of the commercial internet and is therefore outdated.
"People do not give up their rights when they move their private information from physical storage to the cloud," Microsoft says in the lawsuit, a copy of which was seen by Reuters.
It adds that the government "has exploited the transition to cloud computing as a means of expanding its power to conduct secret investigations".