Retailers are hoping for a resolution this year from the Supreme Court, which hears arguments Tuesday in a decades-old dispute: Whether companies must collect sales tax on items sold in a state where they don't have a store or other building.

If the court backs government officials who say they're losing billions of dollars in uncollected taxes, thousands of small companies could be forced to start charging their out-of-state customers for them. Some businesses fear that could alienate customers used to tax-free shopping. On the other side: Retailers who do collect sales tax and believe those who don't have an unfair advantage.

The justices will hear online retailers Wayfair, Overstock.com and Newegg challenging a South Dakota law enacted last May requiring out-of-state retailers that have sales of more than $100,000 or over 200 transactions a year in the state to collect sales tax. Their decision could have national implications on e-commerce, although Congress can pass legislation afterward that broadens or narrows the law.