With state revenues decreasing, many states are considering the so-called "Amazon Laws" which require Internet retailers to collect sales tax even if there are based in another state.
The Supreme Court ruled that companies need to collect sales tax only if they maintain a "physical presence" (store or warehouse) in the same state as the customer. New laws get around this Supreme Court ruling by treating "in-state-hosted affiliate websites" as the legal equivalent of a physical presence.
States loose approximately $20 billion dollars a year in tax revenue due to online shopping.
source: PARADE