A "business card" is still an individual person's card: even if there is a business name on the card and the company pays the bills, there is still an individual person (you) responsible for the card. If you had the card and the savings account from the same bank and an agreement you signed with the bank (such as the credit card agreement) gives the bank the right to take funds out of your account for unpaid debts, then they may do this. In this instance, you would have contractually given them the right to take the money.