The banks allegedly failed to tell their customers that the US government would be examining wire transfers sent via the Swift network of banks,
Federal Data Protection Commissioner of Switzerland Hanspeter Thur said the fact that the information could potentially be seen by a third party should have caused the banks to issue a warning to customers.
In June last year reports first emerged that the US government was exercising emergency powers to scrutinise data on some wire transfers passed over the Swift interbank network.
December saw Guy Verhofstadt, Belgian prime minister, state his opinion that the US should have told the Belgian government about the data sharing scheme, and call for talks between the EU and the US to agree on safeguarding data privacy.
Responding, Francis Vanbever denied that Swift had broken data protection laws and voiced its objections to the Belgian Data Privacy Commission's suggestion that it had broken EU and Belgian data protection laws.
