Tech giants including Amazon, Apple and Google have backed Microsoft's fight against a US gagging order.
The trio and Mozilla have filed a brief supporting Microsoft's stance that the US should allow companies to tell customers when the US government asks for their details, which firms store in their respective clouds.
Microsoft began its case against the US government's Department of Justice (DoJ) in April, claiming the 1986 Electronic Communications Privacy Act violates the Fourth Amendment to be informed of searches and seizures.
The tech giant will hope the brief helps its arguments that the Act should be scrapped, with Amazon, Apple, Google and Mozilla also unable to inform their users of any government data requests concerning them.
Apple complied with just over half of UK government data requests in the second half of 2015, and 80% of 4,000 US requests.
Meanwhile Facebook revealed that the UK government asked for 4,489 user or account details between January and June 2015, complying with 78% of those requests.
The brief also has the support of the Electronic Frontier Foundation, Fox News, and others.
However, the DOJ believes Microsoft's lawsuit lacks any legal standing, and that processes already exist to protect people's rights.
Microsoft recently won an appeal in a lengthy court battle with the US government, over access to data stored on a Microsoft server in Dublin. The US had demanded information stored on that server in relation to a drug trafficking case.
However, Microsoft - and other vendors - wants to ensure customers can trust that it will protect their data from government spying.
