It is claimed that the Swiss bank facilitated the transfer of 19,000 wealthy clients' assets to the tiny European nation of Liechtenstein - with the collusion of a local firm.
Senators also slammed the "culture of secrecy and deception" in the nation.
Further allegations in the report include UBS staff being told by bosses to only contact clients via public payphones, in order to make tracing the calls more difficult for authorities.
News of the report follows revelations from an ex-UBS banker, Bradley Birkenfeld, who has pleaded guilty to helping clients hide assets abroad.
"UBS has opened thousands of accounts in Switzerland that are beneficially owned by US clients, hold billions of dollars in assets, and have not been reported to US tax authorities," the report states.