The French and German governments are demanding the United States comes clean over allegations that its intelligence services have been spying on European Union offices, reports the BBC.
A report in Germany's Der Spiegel magazine claims key EU offices in the US and Europe were bugged.
French Foreign Minister Laurent Fabius said that if confirmed, the activities would be "totally unacceptable".
Fugitive ex-CIA analyst Edward Snowden leaked secret papers, Der Spiegel says.
Mr Snowden - a former contractor for the CIA and also the National Security Agency (NSA) - has since requested asylum in Ecuador.
German Justice Minister Sabine Leutheusser-Schnarrenberger said the alleged US behaviour was reminiscent of the Cold War.
"If the media reports are accurate, then this recalls the methods used by enemies during the Cold War," he was quoted as saying by the Associated Press news agency.
"It is beyond comprehension that our friends in the United States see Europeans as enemies."
Meanwhile, the president of the European Parliament, Martin Schulz, said he was "deeply worried and shocked" by the allegations.
He said any such spying could have a "severe impact" on ties between the EU and the US.
Read more of this report from the BBC.