Sidley Austin and other law firms played a large role in the proliferation of tax shelters in the 1990s that cost the U.S. Treasury tens of billions of dollars.

http://articles.chicagotribune.com/2005-02-12/business/0502120209_1_sidley-austin-brown-tax-shelters-wood-llp

https://dealbook.nytimes.com/2010/02/04/us-report-details-money-laundering/