See the mess that happened in Cyprus a few years ago, with bank accounts frozen for a couple of weeks & money effectively stolen from them by the government.
(Ok, the government called it a "tax" on all accounts with the two main banks, which were both on the verge of going bust before the government stepped in. But no-one had ever imposed such a "tax" before or even discussed such a thing. And the government had guaranteed that bank balances below a certain amount (100,000 Euros) would be 95% guaranteed even if the bank went bust, and the "tax" broke that guarantee. The government eventually partly backed down because of that, and only "taxed" people with more than the guaranteed amount. But it's still a scary precedent).