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. 

The increased enforcement on the wealthy shouldn't come as a surprise. 

IRS Commissioner Douglas Shulman said in late 2009 that the IRS had formed a "global high wealth industry group" to target "high-wealth individuals." 

He said the unit would start with a "small number" of audits and add agents with "specialized skills and expertise" over time. 

A separate report, while not breaking down the makeup of the high-wealth unit, showed that the total number of IRS enforcement agents grew last year by about 1,650, to a total of 22,710. 

Overall, the IRS collected close to $58 billion through enforcement efforts in 2010 -- up from $34 billion a decade ago, when audits were done on about 0.6 percent of all individual returns.