NEW YORK - The US Justice Department is investigating whether Credit Suisse Group continued to help American clients hide assets from the authorities, eight years after the bank paid a US$2.6 billion (S$3.7 billion) tax evasion settlement and pledged to tackle the issue.

Investigators are examining whether the bank aided United States account holders, particularly with South American passports, who may not have told the Internal Revenue Service (IRS) about assets totalling hundreds of millions of dollars, according to sources familiar with the matter. Former bankers blew the whistle on the bank, court records show.

Credit Suisse's main banking unit pleaded guilty in 2014, admitting it helped thousands of Americans evade taxes. It paid US$2.6 billion under that deal, which required it to close "any and all" US accounts not declared to the IRS.

The Zurich-based bank denies improper conduct, and says it is cooperating with the US authorities.

"Credit Suisse does not tolerate tax evasion," the bank said in a statement. "We have implemented extensive enhancements since 2014, to root out individuals who seek to conceal assets from tax authorities. Our clear policy is to close undeclared accounts when identified, and to discipline any employee who fails to comply with bank policy or falls short of Credit Suisse's high standards of conduct."

The investigations add pressure on a bank seeking to deliver a strategy that will revamp its risk culture, downsize its unprofitable investment bank and return it to profitability. Credit Suisse may sell parts of its Latin American wealth management business and severely decrease or further exit businesses in its investment bank. The stock has declined by about two-thirds since scandals surrounding Greensill Capital and Archegos Capital Management early last year.

Repeat offenders

Deputy US Attorney General Lisa Monaco has vowed to crack down on repeat corporate offenders, but it is unclear whether the Justice Department will take action against the bank, such as with new charges or a financial penalty.

The bank's outside attorneys have made their case to prosecutors in Washington, arguing it broke no laws and deserves no further punishment, according to the sources, who were not authorised to discuss the matter publicly.

They have also met with investigators from the US Senate Finance Committee, which will issue a report in the coming weeks.

The Justice Department declined to comment. In a court filing last year, its prosecutors cited "ongoing law enforcement activities" related to the bank's plea deal, and "discussions with Credit Suisse regarding the identification and remediation of remaining Swiss accounts held by US citizens."

US taxpayers are supposed to pay taxes on income anywhere in the world, and foreign banks must notify the IRS about American accounts.

The Senate Finance Committee, led by Oregon Democrat Ron Wyden, is also preparing a report that will discuss how the bank vetted dual citizens.

Complex IRS rules can cause confusion at banks trying to determine if accounts are controlled by US residents, the sources said.

The committee has been investigating information "suggesting that Credit Suisse continued to serve US citizens hiding undeclared accounts offshore", Mr Wyden said in a statement.

"Any systemic failures to crack down on undeclared US accounts by the bank would be a clear violation of its plea deal with the Justice Department."

In the light of the Justice Department pledge to crack down on repeat corporate offenders, "this case demands full investigation and accountability", Mr Wyden said.

BLOOMBERG