Former Credit Suisse Group AG bankers who blew the whistle on their employer for helping wealthy Americans dodge taxes are now urging U.S. authorities to punish the bank beyond the $2.6 billion it paid as part of a guilty plea seven years ago.

A lawyer for the bankers wrote a letter to the Internal Revenue Service’s whistle-blower’s office last week that said the bank’s conspiracy continued “well after the plea agreement and sentencing” in 2014. Credit Suisse’s “misrepresentations and material omissions” about one wealthy American caused the bank to violate its plea agreement after the Justice Department and IRS agreed to reduce its fine by $1.3 billion, wrote the attorney, Jeffrey Neiman.