Ripples of anxiety are likely to be coursing through internet retailers this month. That's because two events - the introduction of the Marketplace Fairness Act in the U.S. Senate and an opinion written by Supreme Court Justice Anthony Kennedy - made it more likely than it has been in 50 years that they will have to collect taxes in states where they don't have a physical presence. If that happens, out-of-state retailers would be compelled to collect sales and use taxes in almost 10,000 state tax jurisdictions that, according to the Tax Foundation, exist across the United States.