Seven years after Credit Suisse promised federal prosecutors that it would stop helping rich Americans hide their wealth from tax collectors, a whistle-blower is contending that it continued to do just that, raising the possibility that the Swiss bank could face a fresh investigation and steep financial penalties.

The allegations, laid out in documents sent last week to the Justice Department and the Internal Revenue Service, were made by a former Credit Suisse employee who said that the bank continued to hide assets for its clients long after it promised prosecutors it would close those accounts, according to copies of documents obtained by The New York Times.

The whistle-blower, whose identity is unknown, is also contending that Credit Suisse lied to federal prosecutors, the Internal Revenue Service and members of Congress during their yearslong inquiry into how Swiss banks helped Americans defraud the government. Those investigations ultimately led to a settlement in May 2014 between Credit Suisse and federal prosecutors, in which the Swiss bank pleaded guilty to helping some of its American clients evade taxes by cloaking their wealth through offshore shell companies.