Dozens of allies threw their weight behind Microsoft on Friday in a case that challenges law enforcement's use of secrecy orders to cloak its pursuit of digital communications in investigations.
Amazon, Google, Snapchat, Salesforce and several others filed a brief on Friday in support of Microsoft in its case against the United States Justice Department, while Apple, Mozilla and others made their own filing. Civil liberties groups and media organizations like Fox News, National Public Radio and The Washington Post submitted their own briefs.
Microsoft was also backed by a collection of law professors and a group of former United States attorneys who worked in the Western district of Washington, where Microsoft filed its federal lawsuit in April.
Microsoft's effort to rally support is part of a growing resistance by technology companies to government attempts to snoop on the electronic communications of their customers.
Revelations by Edward J Snowden, the former United States government contractor, about the extent of electronic surveillance by spy agencies have rattled technology companies, which worry that trust in their products is being undermined.
In a statement, Brad Smith, Microsoft's president and chief legal officer, said the company was grateful for the support from what it expected to total 80 signatories on multiple briefs by the end of the day. He noted the diversity of backgrounds of the signatories, saying, ''it's not every day that Fox News and the ACLU are on the same side of an issue.''
''We believe the constitutional rights at stake in this case are of fundamental importance, and people should know when the government accesses their emails unless secrecy is truly needed,'' Smith added.
Peter Carr, a spokesman for the Justice Department, declined to comment.
The lawsuit argued that the government's use of a provision of the Electronic Communications Privacy Act of 1986 - which prevents Microsoft from notifying customers when their communications have been turned over to law enforcement, sometimes indefinitely - is unconstitutional.
Microsoft said the secrecy orders violated the Fourth Amendment, which grants people and businesses the right to know if the government seizes or searches their property, along with the company's First Amendment right to communicate with its customers.
Technology companies are concerned that secrecy orders are especially troubling in the era of cloud computing. ''In contrast to a search of a home or a seizure of physical property, there may be no way for a user to detect that the provider has disclosed information stored in the account to the government,'' the brief filed by Amazon, Google and others said.
In March, nearly every major technology company, including Microsoft, Amazon and Google, filed briefs backing Apple in a legal showdown with the federal government, which had demanded Apple's technical assistance in bypassing security software on an iPhone used by a gunman in the shootings in San Bernardino, California, last year.
The Federal Bureau of Investigation eventually broke into the phone with the help of an outside party, not Apple.
The Microsoft lawsuit is different in that it does not centre on any individual case, but instead is aimed at the legal process the government uses to keep its information requests secret.
The company said such secrecy orders are becoming more frequent. In its lawsuit, Microsoft said of the more than 5,600 federal demands for customer data it received between September 2014 and March 2016, nearly half were accompanied by secrecy orders that prevented Microsoft from telling affected customers that it had turned over their information to the government.
Microsoft executives have said they appreciate the necessity of secrecy orders in some cases. But they have criticized as too low the bar that prosecutors must meet to obtain a secrecy order from courts.
Microsoft is also concerned about the absence of time limits on when it can disclose to customers that the government has obtained their communications. For physical searches of files and the like, most secrecy orders delay notification for a limited period of time, often one to three months.
For the government data requests with secrecy orders that Microsoft received in the period it examined between 2014 and 2016, more than 68 per cent contained no fixed end date.
''Law enforcement officials have no practical need to keep their searches secret indefinitely, except in the rarest of circumstances, which must be supported by particularised need,'' read the brief filed Friday by former United States attorneys supporting Microsoft.