(Wall Street Journal) — Amazon.com Inc., the world’s largest online retailer, hasn’t charged sales tax in most states since its founding in 1994. And it has taken some extreme measures to keep it that way. Among them: Staff traveling around the U.S. have been required to first consult a company map that shades each state red, yellow or green, said three people who have worked for the retailer. These people said they needed permission from managers or company lawyers before entering “red” states because a worker’s actions might trigger laws that force Amazon to collect taxes in those states. Such steps to avoid local levies allow Amazon to undercut in-state retailers by the amount they must add in sales tax, which can exceed 8%.