The UK government has sought to reassure MPs that their data on Microsoft's servers in the Republic of Ireland cannot be accessed by US surveillance agencies.
William Hague, the leader of the House of Commons, said there's nothing to fear after an MP said he was concerned about the security of parliamentary data stored on Microsoft's cloud-based servers in Europe - despite the migration of MPs' and peers' mailboxes to Office 365 cloud servers in July 2014.
In a letter responding to concerns raised by John Hemming, MP for Birmingham Yardley, Hague wrote: "The relevant servers are situated in the Republic of Ireland and the Netherlands, both being territories covered by the EC Data Protection Directive.
"Any access by US authorities to such data would have to be by way of mutual legal assistance arrangements with those countries."
The foreign secretary implied that MPs' emails would not be accessible by US surveillance agencies because US courts can't override the EU data protection regulations.
"The US authorities could not exercise any right of search and seizure on an extraterritorial basis," said Hague.
But Hague's assurances have been called into question after a US court found Microsoft in contempt for refusing to hand over copies of emails, stored on a server in Dublin, to the US government.
US authorities issued a warrant in December 2013 to access emails the US government says it believes to be linked to drugs trafficking.
In July 2014, US federal judge Loretta Preska ruled Microsoft had to comply with the data access request because it is a US company in control of the data.
The ruling is being appealed by Microsoft and taken to the US Supreme Court.
"Microsoft believes you own your email no matter where it is stored. That's why we've gone to court to ask the US government to follow long-established, internationally agreed upon processes to obtain emails it is seeking as evidence in a case involving a customer account in Ireland," said Microsoft.
"A district judge in New York today issued an order clearing the way for Microsoft to pursue its case against the US government on appeal. The government has demanded that Microsoft turn over customer emails held in its data centre in Dublin, Ireland.
"While the order today holds the company in contempt for not complying with the court's previous ruling to turn over the emails in question, it does not impose any sanctions while the case proceeds to the appellate court, as agreed to by the parties".
The fact that US authorities are trying to access data in Ireland is a cause for concern, according to Hemming.
Hemming, an IT specialist, said: "William Hague says in his letter that US agencies can't search and seize extraterritorial data. But the Microsoft case demonstrates that in fact they are doing that.
"MPs should be aware that the legal position in terms of the security of their emails is either unsure or that American security services can get copies of them if they want them."
Should Microsoft be let off then there will likely be implications for the security of all other extraterritorially stored data.
MPs and peers saw their mailboxes migrated to Microsoft's Office 365 cloud servers in July 2014.
Under parliamentary law, British security services are not allowed to access the emails of MPs.