The court decided to grant UBS "party status", allowing it to access the files and be served with all final decisions by the Swiss federal tax administration (FTA) following a request from French tax authorities to transmit clients' tax data in May.

The FAC said the bank should be given "party status" in part because: "The unusually high number of clients concerned by the request for administrative assistance could leave one with the impression that UBS systematically helped clients to evade taxes."

It also said the compilation of the data sets would mean a lot of work for UBS and "the data might be used in criminal proceedings already launched against UBS in France".

In 2014, French authorities placed UBS under formal examination over whether it helped clients avoid tax and investigating judges ordered the bank to provide bail of 1.1 billion euros.

UBS said in July it had been ordered by the FTA to provide France with tax information and was planning to ask the FAC to look at the request. It also said at the time the legal basis for the request was ambiguous and that the data and the justification received as part of the request lacked the required specificity.

(Reporting by Silke Koltrowitz; Editing by Mark Potter)