A credit card company can lower your credit limit even while you still owe money on the account. The debt does not disappear, and the issuer does not simply erase the balance to match the new limit. Instead, you can suddenly find yourself owing more than the amount of credit the card now allows you to use.
That creates an awkward situation. A card with a $10,000 limit and a $4,000 balance looks very different from the same card with the limit suddenly reduced to $4,000. The balance stayed put, but the breathing room vanished. The Consumer Financial Protection Bureau confirms that issuers generally can reduce a credit limit, including to an amount that leaves no available credit.