From the summary:
Marking the second anniversary of the Supreme Court’s decision in the Citizens United vs. Federal Election Commission case, this report takes a hard look at the lobbying activities of profitable Fortune 500 companies that exploit loopholes and distort the tax code to avoid billions of dollars in taxes.
We identify the “Dirty Thirty” companies that were especially aggressive at dodging taxes and lobbying Congress. These companies so deftly exploited carve outs and loopholes in the tax code that all but one of them enjoyed a negative tax rate over the three year period of the study, while spending nearly half a billion dollars to lobby Congress on issues including tax policy. Altogether they collected $10.6 billion in tax rebates from the federal government.