FATCA, for example. It forces all foreign banks with US customers to report their customers and their assets to the US treasury or suffer a 30% withholding tax

FATCA, for example. It forces all foreign banks with US customers to report their customers and their assets to the US treasury or suffer a 30% withholding tax on all US sourced payments [1]. Needless to say, non-compliance is not a real option for most banks, given the importance of the US in the banking sector, so they're essentially being blackmailed into compliance. (Unfortunately for US expats, some foreign banks figured out that the easiest way to be compliant was simply to get rid of their US customers.) [1] https://www.law.cornell.edu/uscode/text/26/1471 https://www.law.cornell.edu/uscode/text/26/1471