Microsoft is suing the US government over a privacy row. The tech giant has mounted the legal challenge over the right to inform its customers when a federal agency is looking at their emails.

Microsoft says Washington is violating the American constitution - its legal papers read, "People do not give up their rights when they move their private information from physical storage to the cloud."

It continues to say that the US government "has exploited the transition to cloud computing as a means of expanding its power to conduct secret investigations."

A spokesperson told Reuters that the US Department of Justice is reviewing the filing.

The tech giant says that the requests from the US state contravene the Fourth Amendment which affords citizens the right to know if the government searches or seizes their property - it also argues that it encroaches on the First Amendment right to free speech.

This is the latest front in the on-going battle between US tech companies and government agencies in the US concerning how much user data should be made available for security purposes.

So far Apple has led the pushback against the state, this suit from Microsoft indicates that it intends to play a more prominent role in this debate.