The only time when it is lawful to give away client date under the present regime is in tax fraud cases.

The treaty, which would be a new milestone for banking secrecy in the Alpine state, was embraced by a 116-51 vote. The Swiss upper house voted in favour at the end of last year.

The Swiss parliament will, however, make its final decision today when amendments have been debated.

Detractors of the tax plan argue that it will undermine the country’s banking secrecy laws, which have contributed to the success of the financial industry that is crucial for the Swiss economy.

Proponents of the treaty believe, however, that it will ease some of the immense pressure the country is under from the revenue-hungry US.

Because of the relentless crackdown on offshore tax evasion, many private banks in Switzerland and other parts of Europe have decided to turn down US business. UBS, Julius Baer, HSBC and C Hoare & Co are some of the European players that have stopped providing offshore banking to US clients.

After it emerged that Wegelin & Co was being investigated by US authorities for allegedly aiding wealthy Americans to evade taxes, the venerable private bank was sold to Raiffeisen in January this year for an undisclosed sum.

The Swiss financial regulator said at a meeting in December that Swiss bank secrecy cannot survive in its current form.