Brussels reacted furiously on Friday to claims that British and US intelligence agencies spied on the European commissioner in charge of sensitive antitrust cases, including one involving Google.
Joaquín Almunia, the EU's competition commissioner, has access to highly confidential commercial information: he is charged with breaking up cartels, approving mergers and imposing fines on those who break the bloc's antitrust rules.
The claim that Mr Almunia was on the surveillance list of UK and US spy agencies follows news earlier this year that Angela Merkel, German chancellor, had also had her private phone calls targeted.
Mr Almunia was said by European Commission officials to be "upset" by the claims, with particular anger in Brussels being aimed at Britain, whose relationship with the EU executive has grown tense.
Although he did not address the issue specifically at his end-of-year press conference on Friday, President Barack Obama acknowledged that the US "would have to provide more confidence to the international community" about its spying.
"Just because we can do something doesn't mean we necessarily should," said Mr Obama.
The news about Mr Almunia is especially embarrassing, as the US has criticised countries like China for economic espionage while insisting it does not itself spy for the commercial benefit of domestic companies.
An expert panel appointed by the White House to review US intelligence, which reported to Mr Obama this week, said programs should not be directed to "illicit or illegitimate ends, such as the theft of trade secrets or obtaining commercial gain for domestic industries".
Mr Almunia was at the eye of the eurozone storm as EU monetary affairs commissioner before switching in 2010 to the competition brief, where he has presided over antitrust cases involving Google and Microsoft and cracked down on banks suspected of rigging global interest rate benchmarks.
In other prominent cases involving US companies, the Spanish politician blocked the NYSE's planned takeover of Deutsche Börse and UPS's bid for TNT. His scrutiny of state support for the UK's planned Hinkley Point nuclear plant has been a matter of keen interest to the British government.
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A commission spokeswoman said: "This is not the type of behaviour that we expect from strategic partners, let alone from our own member states."
The claims come as part of a joint investigation by the Guardian, Der Spiegel and the New York Times based on revelations from documents dated from 2008 to 2011 and leaked by Edward Snowden, the former US National Security Agency contractor.
The Guardian reported that British and US intelligence agencies had a list of surveillance targets including Mr Almunia, German government buildings in Berlin and overseas, and charities working Africa.
It also cites one document from Britain's GCHQ eavesdropping centre, drafted in 2009, which makes clear that it was targeting an email address listed as belonging to "the Israeli prime minister". Ehud Olmert was in was in office at the time.
The collaboration of GCHQ with the NSA in targeting Germany will be embarrassing to David Cameron, British prime minister, who has sought to foster a warm relationship with Ms Merkel.
But the targeting of the European Commission by British spies will be equally damaging; Mr Cameron will have been relieved that the latest leaked documents only emerged hours after he left an EU summit in Brussels on Friday.
Hours earlier Mr Cameron was involved in a row with the commission after Downing Street announced he would challenge plans for an EU surveillance drone programme at a summit in Brussels. A spokesperson for the commission said it had no plans to own or buy drones.
"They've been caught with their pants down," said one Brussels official. "They're not exactly in a comfortable position." Privately, many in the commission's Berlaymont building suspected they were the target of industrial espionage.
Downing Street declined to comment.
Despite Washington's protestations that it does not conduct commercial espionage, the US intelligence's top-secret budget, also leaked by Mr Snowden, set aside money for spying to track other countries' adherence to trade agreements.