An IRS probe was under way for large conservative tax-exempt groups such as Crossroads and Americans for Prosperity, which is funded in part by the oil and gas tycoons David and Charles Koch.

At issue is whether certain outside political groups are spending too much of their money on political activity. Groups incorporated under the 501(c)4 section of the tax code, which are also known as “social welfare organizations,” are tax-exempt and cannot have politics as their primary purpose

Like Super PACs, tax-exempt political groups can raise and spend unlimited funds - in contrast to political campaigns, which may receive only $2,500 per donor each election cycle.

Super PACs, which must disclose their donors, operate independently from campaigns but may release ads that boost or attack specific candidates.

Tax-exempt groups, meanwhile, can qualify under the U.S. tax code as social welfare groups, which allows them to keep their donors private as long as most of their money is spent on so-called “issue ads.” Unlike regular political ads, such ads cannot use a candidate’s name or likeness and are supposed to be used to educate the public on broad issues or positions.

(Source: sarahlee310, via truth-has-a-liberal-bias)