One year ago, prosecutors issued a warrant for emails stored by Microsoft in an Irish data centre, in connection with a drug-related investigation.
The tech giant refused to comply but was ordered by a judge to hand over the information in July.
Microsoft has now filed letters of support from a large number of allies.
These include tech firms Verizon, Amazon, Cisco and HP, as well as trade associations such as the US Chamber of Commerce, and Digital Rights Ireland.
Various news organisations such as CNN, the Guardian and the Washington Post are on board along with computer scientists from universities across the US including Harvard, Stanford and the Massachusetts Institute of Technology.
Earlier this year, New York judge James Francis said that a warrant for online information was the equivalent of a subpoena and had to be obeyed.Privacy rights
The firm and its supporters argue that the centre in Dublin is outside US jurisdiction, while the prosecutors claim that as the data itself is accessible by the firm from within the US, this does not apply.
"We believe that when one government wants to obtain email that is stored in another country, it needs to do so in a manner that respects existing domestic and international laws," wrote Microsoft's Brad Smith, general counsel and executive vice president of legal and corporate affairs, in a blog post.
"In contrast, the US government's unilateral use of a search warrant to reach email in another country puts both fundamental privacy rights and cordial international relations at risk."