With Tax Day approaching, wealthy Americans might want to take extra care with their returns.

Government statistics show the IRS followed through in a big way last year on its pledge to aggressively audit wealthy taxpayers, ratcheting up enforcement for individuals making over $500,000 a year.

Individual audits were up overall in fiscal year 2010 by about 10 percent -- or 1.11 percent of the total number of returns, according to the most recent IRS enforcement report. But the extra audits were stacked at the top of the income scale, where IRS agents no doubt see a bigger potential trove of unpaid tax dollars.

For people making $10 million and up, the swath of those audited rose from 10.6 percent to 18.4 percent. That rate rose from 7.5 percent to 11.6 percent, for those making between $5 million and $10 million. Even those making $500,000 and up got audited more frequently last year, compared with a year prior.