The French subsidiary of UBS has been formally put under investigation in a tax evasion case, the Paris prosecutor's office says.
Spokeswoman Agnes Thibault-Lecuivre said the bank is being investigated for complicity in illegal business dealings.
Three executives at the French subsidiary are already under investigation for allegedly helping rich customers in France avoid the taxman.
UBS said it had been expecting this step as part of the ongoing investigation and is fully cooperating. It denies any wrongdoing, saying it complies fully with French law.
UBS has already been in the spotlight this year as one of the banks where France's then-budget minister hid funds from tax authorities.
A book published last year also alleged that the bank systematically helped French customers dodge taxes.