ZURICH (Reuters) - Switzerland's highest court spelled out the steps foreign authorities must take if they want legal assistance in chasing tax cheats as it released the written verdict on why it made UBS Group (S:UBSG) in July share client data with France.
The Federal Court ruled that Switzerland's biggest bank must hand over historical data on more than 40,000 client accounts to French tax authorities in a landmark case keenly watched by other countries seeking similar information.
The ruling was also closely watched for the impact it might have on the Swiss bank's separate 4.5 billion euro ($5 billion) legal battle with France in a criminal case over alleged tax avoidance by UBS clients.
Revenue-hungry governments, for years thwarted by Switzerland's strict secrecy rules, are monitoring developments to see if they can use historical evidence of their citizens' trying to hide money from tax authorities.
In its written ruling released on Wednesday, the court said it would not help "fishing expeditions" by foreign tax authorities seeking potential evidence of wrongdoing by groups of citizens.
Tax authorities must give a detailed description of the group involved and specific circumstances that led to the request; explain the applicable law and reasons to assume that taxpayers did not fulfill their obligations; and demonstrate that the information requested could help make them do so.
The court reinforced its stance that the client data UBS is providing French tax authorities cannot be used by French prosecutors in the criminal investigation of UBS, the world's biggest wealth manager.
The data is solely to help go after French tax dodgers.
The thousands of accounts in question and the more than 11 billion Swiss francs ($11 billion) they held justified Switzerland's granting legal assistance in this case, the court has said.
"It should be noted that the periods from which the transmitted lists came (2006 and 2008) fall within the period for which UBS is suspected of having set up a comprehensive tax evasion system," it added.
"In this context, it was essential for the French tax administration to carry out systematic checks on the information supplied by the German tax authorities."
German authorities acting on information bought from a leaker had discovered the list of account numbers held by French taxpayers at UBS. The Germans shared the information with France, which wanted names of the account holders to see whether they had properly declared and taxed their foreign assets.
($1 = 0.9073 euros)
($1 = 0.9972 Swiss francs)