Credit Suisse (CSGN.S) breached a 2014 plea agreement with US authorities by continuing to assist ultra-wealthy Americans in evading taxes and concealing more than $700 million from the government, according to the Senate Finance Committee.

Following a two-year probe into Credit Suisse, which agreed to a rescue acquisition by rival UBS (UBSG.S) earlier this month, the committee said it had discovered “serious breaches” of the 2014 deal between the Swiss institution and the US Department of Justice (DoJ) for aiding tax fraud.

New owner UBS or the Swiss government should assume responsibility for any future fines, the committee said, calling on the DoJ and the Internal Revenue Service to investigate whether Credit Suisse should face more penalties.

The violations found by the committee included failing to disclose nearly $100 million in secret offshore accounts belonging to a single family of dual U.S.-Latin American citizens, which it said represented an “ongoing and potentially criminal conspiracy”.