apply in the age of the internet.

The case on Tuesday focuses on businesses' collection of sales tax on online purchases. Right now, under the decades-old Supreme Court rule, if a business is shipping a product to a state where it doesn't have an office, warehouse or other physical presence, it doesn't have to collect the state's sales tax. Customers are generally supposed to pay the tax to the state themselves, but the vast majority don't.

States say that as a result of the rule and the growth of internet shopping, they're losing billions of dollars in tax revenue every year. More than 40 states are asking the Supreme Court to abandon the rule.

Large retailers such as Apple, Macy's, Target and Walmart, which have brick-and-mortar stores nationwide, generally collect sales tax from their customers who buy online. But other online sellers that only have a physical presence in a few states can sidestep charging customers sales tax when they're shipping to addresses outside those states.

Sellers who defend the current rule say collecting sales tax nationwide is complex and costly, especially for small sellers. That complexity was a concern for the Supreme Court when it announced the physical presence rule in a case involving a catalog retailer in 1967, a rule it reaffirmed in 1992. But states say software has now made collecting sales tax easy.

The case the court is hearing has to do with a law passed by South Dakota in 2016, a law designed to challenge the Supreme Court's physical presence rule. The law requires out-of-state sellers who do more than $100,000 of business in the state or more than 200 transactions annually with state residents to collect and turn over sales tax to the state.

The state wanted out-of-state retailers to begin collecting the tax and sued Overstock.com, home goods company Wayfair and electronics retailer Newegg. The state has conceded in court, however, that it can only win by persuading the Supreme Court to do away with its current physical presence rule.