A U.S. Supreme Court ruling last week involving the state of South Dakota vs Wayfair (an online furniture retailer) opens the door for states to impose sales taxes on online retailers located outside their borders.

This will have wide-reaching effects on small businesses and consumers. Here’s what you need to know:

Suppose you retire to a new state with warm weather and lower taxes. If you keep a part-time home in your original state or you later decide to return, you could have a tax problem. State tax authorities may argue you never really left, and that you owe them a big tax bill for all the income you earned while away. Here are tips to ensure this does not happen to you.