The U.S. Supreme Court is scheduled to consider a case next week (South Dakota v. Wayfair, Inc.) that has the potential to significantly improve states and localities’ ability to enforce their sales tax laws on Internet purchases.

Online shopping is hardly a new phenomenon. And yet states and localities still lack the authority to require many Internet retailers to collect the sales taxes that their locally based, brick and mortar competitors have been collecting for decades.

A new ITEP analysis reveals that in seven states (Alabama, Alaska, Idaho, Iowa, Mississippi, New Mexico, and Pennsylvania), the nation’s largest e-retailer, Amazon.com, is either not collecting local-level sales taxes or is charging a lower tax rate than local retailers. In other states, such as Colorado and Illinois, Amazon is collecting local tax because it has an in-state presence, but localities cannot collect taxes from other e-retailers based outside the state.

Online retailer Amazon.com made headlines last year when it began collecting every state-level sales tax on its direct sales. Savvy observers quickly noted that this change did not affect the company’s large and growing “marketplace” business, where it conducts sales in partnership with third-parties and rarely collects tax. But far fewer have noticed that even on its direct sales, Amazon is still not collecting some local-level taxes.