The Supreme Court decision in South Dakota v. Wayfair, Inc., et al. a little over three years ago eliminated the requirement for physical presence in order for the state to require sellers to collect sales tax. Since then, just about all states have passed new laws defining "nexus" for sales tax so that they can require out-of-state sellers to collect sales tax on products shipped into the state. It is usually defined in terms of the number of sales or the dollar amount of sales in the state, but each state has different rules.
The Supreme Court decision is usually referred to as just Wayfair or the Wayfair decision.
