UBS is being investigated in the US over whether it helped Americans evade tax through banned investments.
The BBC reports the Swiss bank is being investigated over the potential sales of “bearer bonds”, which can be transferred without registering ownership and so allowing clients to potentially hide assets.
The investigation is being carried out by the Securities and Exchange Commission and the US Attorney’s Office for the Eastern District of New York.
The bank told the BBC: “We are co-operating with the authorities in these investigations.”
UBS has already paid a settlement of $780m (£512m) in a separate probe by the US Justice Department.
The Swiss bank was among the banks fined in November by UK and US regulators over foreign exchange manipulation. It paid 774m Swiss francs in total, and also paid $300m to settle charges it helped German clients evade tax.
It comes as the pressure mounts over allegations that HSBC’s private Swiss bank helped up to 1,100 British clients avoid paying tax.