Well, specifically, 2004's American Jobs Creation Act, which benefited hundreds of multinational corporations with a huge, one-time tax break. As University of Kansas Prof. Susan Scholz puts it, "We have a situation where we, in essence, invite corporations to buy their own tax rate through lobbying... which ultimately corrupts both the companies and the politicians." From NPR's Planet Money:
In a recent study, researchers Raquel Alexander and Susan Scholz calculated the total amount the corporations saved from the lower tax rate. They compared the taxes saved to the amount the firms spent lobbying for the law. Their research showed the return on lobbying for those multinational corporations was 22,000 percent. That means for every dollar spent on lobbying, the companies got $220 in tax benefits.