Governments have that power already. Various AML legislation can make any high street bank to not only block your account without reason util you prove your innocence, you can't even withdraw any of your money in cash. It happened to me in the UK, my account blocked with no reason for weeks until I summited all documentation. I was a foreign student at the time, almost destroyed me, no money for rent etc.

In any case, it's a orthogonal issue, government power vs democratic accountability, the highly regulated private banking system certainly does not protect you against it, they will do whatever the government asks of them as long as they can maintain their key rent extraction monopolies.