By Nicholas Confessore, The New York Times "The Obama administration on Tuesday moved to issue new rules that would curtail political activity by tax-exempt nonprofit groups, with potentially significant ramifications for one of the fastest-growing sources of campaign spending. The proposed rules, announced by the Treasury Department and the Internal Revenue Service, would expand and clarify how the IRS defines political activity and then establish clearer limits for how much activity nonprofits can engage in. Such a change – long urged by government watchdog groups – would be the first wholesale shift in a generation in the regulations governing political activity. The move to curtail nonprofits follows years of legal and regulatory shifts, such as the Supreme Court’s Citizens United ruling in 2010, that have steadily loosened the rules governing political spending, particularly by big corporations, labor unions and the wealthy . The rules would not prohibit political activity by nonprofit organizations. But by establishing clearer limits for campaign-related spending, the new rules could have a significant effect on the big-spending nonprofit groups that have played a central role in national politics in recent years, spending hundreds of millions of dollars on political advertising and voter outreach. The administration’s proposal would apply to nonprofit groups organized under Section 501(c)4 of the tax code, which are permitted tax exemption in exchange for devoting themselves primarily to the promotion of “social welfare,” which under current rules can include some political activity."