There’s a law called FATCA (Foreign Account Tax Compliance Act) that attempts to force foreign banks to report assets and information on foreign accounts held by US citizens. Since US law doesn’t really have dominion over foreign companies, the way they force compliance is to say that any bank that doesn’t comply will be forbidden from interacting with the US Wire Transfer system (FedWire). Without that, those banks will not be able to do correspondent business with US banks, which would have significant negative consequences if they do any international business. So, yeah, big brother is watching - even outside the US.