Over 20 tech firms including Apple, Amazon and AT&T have joined Microsoft in a legal battle with the US government over accessing user data stored overseas.

10 groups are filing their "friend of the court" briefs in New York today, with the ten briefs signed by 28 leading technology and media companies, 35 leading computer scientists, and 23 trade associations and advocacy organisations.

Microsoft points to the briefings as proof that the case in question involves not a narrow legal question, but a broad policy issue that is fundamental to the future of global technology.

The latest effort in the long-running court battle has taken pace following the leaks about the US NSA’s bulk electronic data collection.

In July, a US judge ruled that Microsoft has to turn over users’ emails from its data centre in Ireland to federal prosecutors, as per a criminal search warrant.

Appealing the ruling, Microsoft noted that the US authorities have no right to automatically compel US firms to surrender customer data stored overseas.

Microsoft head lawyer Brad Smith said in a statement: "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."

"In contrast, the U.S. 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. "And as today’s briefs demonstrate, the impacts of this step are far-reaching."

However, the US government is yet to file its reply to Microsoft’s appeal, and oral arguments on the issue are not anticipated for more six months or so, according to Reuters.

US-based provider of cloud security and enablement services Skyhigh Networks’ European spokesperson Nigel Hawthorn said this will be a watershed moment for cloud computing.

"Forget nudegate and the Sony hack, the current Microsoft case against the US government will shape the future of cloud computing. I’m glad recent developments have got people talking about the issue as it’s a story that every person and organisation should pay close attention to.

"It highlights fundamental issues relating to the legal jurisdiction of the cloud, as well as the difficulties facing single government and legal bodies that try to impose their laws on the internet, a global entity beyond their reach. Governments and legal systems need to realise their limitations in this regard, as taking a legal sledgehammer to cloud computing could break it for good."