Microsoft is suing the US government over the right to tell its users when federal agencies want access to private data.
It say keeping access requests secret is against the US constitution, which states that individuals should be made aware if the government searches or seizes their property.
Microsoft said 5,624 requests for data were made in the past 18 months, and almost half came with a court order forcing the company to keep the demand secret.
"People do not give up their rights when they move their private information from physical storage to the cloud," Microsoft said in the lawsuit, according to the Reuters news agency.
Microsoft added that it felt the government "exploited the transition to cloud computing as a means of expanding its power to conduct secret investigations".
The US Department of Justice has not yet commented on the row.
This is a developing story - more to follow.