Swiss bank UBS is being sued for more than $US2 billion amid claims it concealed the Ponzi scheme of fraudster Bernard Madoff that cost clients billions.
Irving Picard, who is acting as trustee for Madoff's victims, lodged the lawsuit.
He argues UBS put its own gain ahead of protecting investors, collecting $US80 million in fees and giving the scheme an air of legitimacy.
Forbes magazine national editor Robert Lenzner says the accusations are serious.
UBS says the charges are completely unfounded and without merit, and it will defend itself.
Madoff was sentenced to 150 years in prison.