EU Commissioner for Justice Viviane Reding has raised her concerns over the Prism surveillance information-sharing programme with the US Attorney General Eric Holder, who she is to meet in Dublin on Friday.
In a statement on her website, Reding cited the important of trust and privacy to individual citizens, companies, and the wider digital economy.
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"The respect for fundamental rights and the rule of law are the foundations of the EU-US relationship," she began.
"This common understanding has been, and must remain, the basis of cooperation between us in the area of Justice. Trust that the rule of law will be respected is also essential to the stability and growth of the digital economy, including transatlantic business. This is of paramount importance for individuals and companies alike."
The Prism programme apparently gives the US National Security Agency and the FBI access to data from Google, Microsoft, Facebook, Apple, Yahoo and Skype, though each firm denies that it has given any agency access to its servers.
The controversy arose when former CIA employee Edward Snowden stated that US agencies gathered and shared data on the public's phone and internet use.
Google has responded to the controversy by publishing a letter it claims to have sent to both US Attorney General Holder and the FBI, in which it states that whilst it complies with legal requests for information, that does not extend to 'unfettered access' to its data.
"Assertions in the press that our compliance with these requests gives the US government unfettered access to our users' data are simply untrue. However, government nondisclosure obligations regarding the number of FISA national security requests that Google receives, as well as the number of accounts covered by those requests, fuel that speculation."
Reding sent a letter to Holder earlier this week, in which she put forward seven areas of concern:
Are they only aimed at gathering the data of US citizens and residents, or are they also - or even primarily - targeting non-US nationals, including EU citizens? Is the data collection limited to specific and individual cases and, if so, what criteria is applied? How regularly is the data of individuals collected or processed in bulk? What is the scope of Prism and other such programmes? Is it limited to national security and foreign intelligence, and if so how are such terms defined? How might companies in the US and EU challenge the efforts to access and analyse the data? What ways might EU citizens find out if they have been affected? How is this different to the situation for US citizens and residents? How might EU citizens and companies challenge any effort to access and process their personal data? How does this compare to the rights offered to US citizens and residents?