Switzerland has reportedly handed over to French authorities documents on 300 UBS customers suspected of evading taxes
A report in the SonntagsZeitung newspaper said that the documents have been dispatched to judicial authorities in Paris.
The report added that affected customers have not been informed.
French investigating magistrates have proposed that UBS pay a €4.88bn (£3.83bn, $6.13bn) fine in a probe into whether the Swiss bank helped rich French individuals evade taxes, Reuters reported earlier in the month.
Swiss Tax Rules
The delivery of the UBS documents was made possible by the recent revision to Swiss tax rules, which makes it easier for other countries to extract information on suspected tax dodgers.
The revision to the Swiss Tax Administrative Assistance Act eliminated the need to inform individuals before any details about them were shared with a foreign jurisdiction for assumed tax crimes.
German and US Probes
In July, UBS agreed to pay €300m to settle an investigation into whether it helped German clients evade taxes.
In 2013, a French prosecutor put the UBS head office and its subsidiary in France under formal investigation on charges of illegal sales practices and complicity in illegal sales practices, respectively.
French judicial authorities visited the bank's Paris headquarters in November 2013.
A large proportion of the first world's private wealth has traditionally been safely hidden in Switzerland.
An unrelenting assault on once-hallowed Swiss banking secrecy began in 2007 at UBS, which later agreed a $780m deferred prosecution agreement with the US.