Microsoft said it plans to argue that the warrant, which would require the tech giant to turn over customer emails stored in a data center in Dublin, should be nullified because it would give US government excessive power to pry over private information.

The case comes amid rising concern about US surveillance following revelations of snooping disclosed by former National Security Agency contractor Edward Snowden. Leading tech firms, including Apple and Verizon, have filed briefs supporting Microsoft.

Microsoft general counsel Brad Smith said the customer emails, sought in this case in a Justice Department narcotics probe, should be entitled to the same protections as paper letters sent by mail.

That means prosecutors should only be able to access the information in the electronic ‘cloud’ with a warrant.

"But under well-established case law, a search warrant cannot reach beyond US shores," Smith said.

Smith also said the case could leave US citizen's privacy vulnerable to overseas prying, writing "it's hard to believe the American people will blithely accept that foreign governments can obtain their emails stored in US data centers without letting them know or notifying the US government."

But US Attorney Preet Bharara argued that under a 1986 law governing electronic communications, the tech giant is required to produce the data regardless of where Microsoft has decided to store it.

"Nothing in the text or structure of the statute carves out an exception for records stored abroad, and none exists in precedent," Bharara said in a court brief.

Wednesday's hearing will focus on Microsoft's appeal of Francis's decision and will take place in US District Court in downtown Manhattan.

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