Staffing cuts at the IRS resulted in a record low number of audits during the 2015 filing season, as well as record-low audit revenue, according to USA Today. Audits of tax-exempt organizations and corporations with at least $10 million in assets both dropped to their lowest levels in 10 years. Because of this, revenue generated from these audits has dropped to a 13-year low: $7.32 billion. 

This is part of an overall trend towards reduced enforcement. Last year saw audit rates of individual taxpayers drop to a 10-year low of its own, according to a 2015 USA Today article. IRS Commissioner John Koskinen said last fall that there's a less-than-1-percent chance a tax return will ever be checked for accuracy, according to CBS News.  

But not all audit coverage is shrinking: audits of high-income taxpayers have actually been growing, according to The Wall Street Journal. Last year the IRS audited 10 percent of returns showing $1 million or more of income, compared with 7.5 percent the previous year, and 5.3 percent in 2006. CNBC attributed this to the IRS's forming a new unit in 2009 that focused specifically on high-earning taxpayers, saying the group has become more aggressive since its formation.