According to their LM-2 (filed with the Department of Labor), they spent $42 million on politics. But according to their tax return with the IRS, they spent nothing. Why would they report differently to different federal agencies? It turns out that union expenditures on politics are taxable.
The Alliance for Worker Freedom estimates that the AFL-CIO owes $14 million in back taxes. They really are trying to emulate Al Capone.