Billions of dollars of goods sold each year by independent merchants on Amazon.com and other online marketplaces would be vulnerable to state sales taxes for the first time if justices decide to reverse a quarter-century-old precedent in a case before the Supreme Court this week.
In the case, South Dakota is seeking to overturn a longtime precedent under which states can’t require retailers to collect sales taxes unless the companies have a physical presence in the state. While Amazon.com Inc. itself collects sales taxes on...