US lawmakers said Wednesday that Credit Suisse broke the terms of a plea deal with US authorities by failing to disclose secret offshore accounts that wealthy Americans used to evade taxes. The lawmakers' statement followed the release of a two-year investigation into the part employees at the troubled Swiss bank played in assisting clients' tax evasion.

A roughly $100 million in accounts belonging to a family of American taxpayers that the bank failed to declare are linked to an ongoing, potentially illegal conspiracy, according to the US Senate Finance Committee. A US businessman was allegedly aided by Credit Suisse to conceal more than $220 million in offshore accounts from the IRS.

According to the committee, Credit Suisse disclosed that it had discovered 23 accounts, each worth more than $20 million, that had not been reported to tax authorities. Many of these accounts had only recently come to light. According to its findings, the bank broke the terms of a nine-year-old plea agreement with the US Justice Department by concealing more than $700 million.

“Credit Suisse got a discount on the penalty it faced in 2014 for enabling tax evasion because bank executives swore up and down they’d get out of the business of defrauding the United States,” said Sen. Ron Wyden, the Democratic chairman of the committee.

In light of recent upheaval in the global financial system, the Swiss government pushed for a $3.25 billion buyout of the long-struggling Credit Suisse by rival bank UBS. Wider concerns sparked by the failure of two American banks caused consumers to withdraw their money, sending shares of Switzerland's second-largest bank tumbling.

On the same day that UBS selected a new CEO to assist with the takeover, the Senate findings present fresh challenges for the company as it attempts to merge with Credit Suisse and form a single Swiss megabank. Also, it is Credit Suisse's most recent run-in with US authorities after settlements for hundreds of millions of dollars regarding the mortgage-backed securities that caused the financial crisis of 2008 were reached.

Credit Suisse said it "does not tolerate tax evasion" and insisted that the Senate report described "legacy issues" — some dating to a decade ago — that have been addressed since. Credit Suisse's years-long problems range from hedge fund losses to fines for failing to prevent money laundering by a Bulgarian cocaine ring.