Swiss authorities have handed over to US authorities data on about half of the 4,450 American clients of Swiss bank UBS who were suspected of tax evasion by an August 26 deadline.
But, the federal finance department indicated that the US and Switzerland had agreed to prolong the handover into the autumn under a deal to avert a threatened US lawsuit against one of Switzerland's biggest banks.
The handover, which marks a softening of Switzerland's coveted banking secrecy, is the cornerstone of an accord the two governments struck in August 2009 on the tax evasion case.
The Swiss finance department said Swiss and US officials were holding talks about 'the final stage' of the agreement's implementation.
The US Internal Revenue Service warned in June it was ready to renew legal action if Switzerland failed to meet the terms of the August 2009 deal obliging UBS to provide the names of customers allegedly dodging American taxes.
US tax authorities started their offensive against UBS in 2008 after questioning a former banker, prosecuting the bank through US courts and forcing it to hand over 300 client names and pay a $780m fine.
The IRS subsequently threatened the Swiss bank, which by then was struggling to survive the global financial crisis, with more litigation over another 52,000 suspected tax evaders.
The lawsuit was averted after the Swiss government intervened to negotiate a settlement with Washington, fearing permanent damage to Switzerland's then biggest bank that could have undermined its whole banking system.
