The management commission of the lower house of parliament said in a statement it had "opened an investigation into the decisions taken by the government on January 18th and April 4th 2012 concerning the transfer of bank data and data on bank employees to US authorities."

In an unprecedented move, the Swiss government gave 11 Swiss banks the go-ahead to accommodate Washington and hand over the names of thousands of their staff and consultants working with American clients.

In addition to providing personal information about staff to the US tax authorities, the banks have also reportedly made available personal documents, emails and details of telephone calls.

The government decision came after Swiss lawmakers approved a revised tax deal with the United States that eased banking secrecy rules, allowing US authorities to more easily obtain details of tax cheats from Swiss banks.

The government's and the banks' actions caused an uproar in Switzerland and especially among the affected bank employees, many of whom have said they no longer dare travel to the United States for fear they could face charges of assisting tax evaders.

The parliamentary commission said Monday it had ordered a probe aimed at casting light on the circumstances surrounding the government decision, and that it would consider whether there should be "consequences."

It did not say how long the probe was expected to take.