Politico has obtained three letters to US clients with accounts at Swiss banks warning them to come clean with the taxman before year-end or face jail time.

The letters come ahead of a New Year’s Eve deadline the U.S. government set for about 300 Swiss banks to take deals protecting them from prosecution. In exchange for confessing and shelling out mountains of Americans’ account information, they’ll get immunity.

Targeting wealthy tax evaders has to be the easiest and most politically popular ways for the US government to raise revenues.