WASHINGTON (AP) - Shoppers heading online to purchase holiday gifts will find they're being charged sales tax at websites where they weren't before.

The reason has to do with the Supreme Court. A June ruling gave states the go-ahead to require more companies to collect sales tax on online purchases. Now, more than two dozen have moved to take advantage of the ruling. Whether online shoppers get charged sales tax comes down to where they live and where they're shopping.

Before the Supreme Court's recent decision, the rule was that businesses selling online had to collect sales tax only in states where they had stores, warehouses or another physical presence. Now, states can force out-of-state sellers to collect sales tax if they're doing a fair amount of business in the state.