You'll love this one.
Go to this link and download IRS Form 211 entitled Application for Reward for Original Information.
If you suspect a local business of using illegal aliens and paying them under the table, narc em out to the IRS. The tax boys can go in, recover all unpaid witholding taxes, plus a 100% penalty, and even fit the miscreant employer with a nice orange jumpsuit.
At the very least you will get that warm fuzzy feeling of doing your civic duty. You may also be awarded up to 15% of the recovered taxes and penalties.
Remember, it was a conviction for tax evasion that finally retired Al Capone...