Can the bank force you to top up an empty account?

Not advisable move by you. As mention the master Mr Lok. Theres a min amount that needs to be kept in the account otherwise there’s a charge. Better check if one time charge or monthly.

If monthly it means you by keeping the account empty you have to pay the bank to keep the account for you, the debt will build up over time. Don’t make any sense at all. Either you top it up till min amount now or you go to the bank to close the account, and only open when you need. Can try asking to waive the fees you owe for empty account. (unless you‘ve kept the account empty for too long, usually they’ll let it go, not sure if theyll waive for closing account though, but no harm trying.)

Legally, the bank have the right to sue you. The min sum and fall below fees are in the legal documents you sign when you open the account. Even if they don’t do anything and you ignore them, this will be in your financial record. Better get this settle before it affects your credit rating. You can always use the min sum as you emergency savings if you keep the account.

There is a fall-below fee (usually $2) if your balance is below a stipulated minimum sum. If that's not enough to deter you, the bank can possibly sue you for not paying back what you owe.