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The German left has been even more outspoken — with some politicians demanding Merkel grant political asylum to Snowden, a technology expert working for a firm subcontracted by the NSA, who was last spotted in Hong Kong preparing to fight US extradition efforts.
Beyond raining on Obama's parade in Berlin, the PRISM affair could have wider consequences for trans-Atlantic relations, making Europeans even more reticent about entering into data-exchange and intelligence sharing deals with Washington.
"The EU must take a strong position on the use of data in the US and ensure that we fight for the protection of our citizens' data," said Claude Moraes, a member of the European Parliament from Britain's Labour Party.
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The EU's Commissioner for Justice Viviane Reding has written to US Attorney General Eric Holder seeking "detailed explanations." The two are scheduled to meet Friday for talks in Dublin.
"European citizens expect 100 percent respect for their fundamental right to have their personal data protected," Reding tweeted.
She also carried a warning for internet companies who collaborated with PRISM and "give priority to US laws over EU fundamental rights."
Tension over the surveillance program could also strain negotiations the US is hoping to start with the Europeans next month with the aim of wrapping up a deal to create the world's biggest free-trade zone by 2015.
Privacy was always going to be a sensitive issue. Now Europeans can be expected to play even harder ball over respect for data protection.
"Any EU-US trade pact will have to fully ensure the highest standards of data privacy for all citizens," said Hannes Swoboda, who heads the Socialist group in the European Parliament.
"It is no good the EU having strict regulation on data protection if those standards are not guaranteed when using US-based internet companies."