Florian Yes, bunq doesn't support a negative balance. The only way you can have a negative balance is by paying for bunq costs. As soon as your balance becomes negative, bunq will start their collection procedure. This procedure may result in a (partial) blocking of your account(s), card(s) and/or API access. If you do not replenish your balance within one month, they may decide to close your account and/or transfer your claim to a collection agency.
So yes, your cards will be temporarily blocked after 25 June, but as soon as your salary arrives you can unblock your cards, as long as this is within a month.