Credit or debit card blocking happens most often when you rent a car or check into a hotel. For example, when you present your credit card, the clerk scans your card and this action may electronically ask the financial institution that issued the card to “block,” or reserve, part of your line of credit to cover the expected costs. If it's a hotel, the amount could be the cost of your room for the length of your stay, plus extra expenses like meals and phone calls you may incur. If it's a car rental, the amount could be the cost of the rental plus refueling.

The Federal Trade Commission (FTC) says the amounts that can be blocked vary widely among merchants. Card blocking is not illegal as long as the amount blocked is in line with what you are likely to pay at the end of the hotel stay or car rental. It you're not close to the credit card limit or account balance threshold, you'll likely be unaware that the block has even been placed.  However, if you are close to your credit limit, the next transaction you attempt may be denied. 

Here are some tips from the FTC:

  • Pay the bill using the same card you presented at the beginning of the transaction, so that the actual charge replaces the block in a day or two. If you use a different card to pay the bill, the block could remain on the original card for up to 15 days.
  • When you check into the hotel or pick up the rental car, ask the clerk how much is being blocked, and how the amount was determined. This will allow you to factor the amount into your spending plans.
  • If you use a different card or cash when it comes time to pay, ask the clerk to remove the block from the original card or call the issuer yourself.
  • If you are trying to select from among potential credit cards, you might want to call the issuers to find out their policies on blocking.