The case you're referring to is
South Dakota vs. Wayfair (Wayfair). It impacts remote sellers, i.e. an entity that does not have property or employees or contractors in a state to which they make sales.
Before Wayfair an entity needed to have a physical presence, property or people, in a state before they had to collect tax on sales shipped to a state.
The Wayfair decision permits states to force entities to collect tax if they have "economic nexus" in that state. Basically, if they make $
X.xx or
y# of sales into a state they have an obligation to collect and remit tax on sales to that state, even if they have no physical presence in that state.
Thresholds can be found here:
Key information such as effective dates, thresholds, and includable sales for out-of-state sellers making sales into states that have enacted economic nexus legislation both before and after the South Dakota v. Wayfair Supreme Court decision.
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