In 1939, the Internal Revenue Service granted tax-exempt status to a group that had been active in New York City politics for years. The agency determined that The Citizens Union of the City of New York earned its status as a social welfare organization, because its primary purpose was furthering the common good.
Over the next seven decades, the IRS would grant tax-exempt status to 1,551 politically active social welfare organizations – hardly a flood of activity among the nearly 1.6 million U.S. charities.
The floodgates opened in 2010, when the U.S. Supreme Court issued its Citizens United ruling, allowing corporations to spend unlimited amounts of money on ads and other efforts to influence voters. More than half of all politically active social welfare organizations – 60 percent -- have been created since then, a MapLight analysis found.