http://www.washingtonpost.com/blogs/the-fix/wp/2013/05/13/what-is-a-501c4-anyway/
The promotion of social welfare does not include direct or indirect participation or intervention in political campaigns on behalf of or in opposition to any candidate for public office. However, a section 501(c)(4) social welfare organization may engage in some political activities, so long as that is not its primary activity. However, any expenditure it makes for political activities may be subject to tax under section 527(f). For further information regarding political and lobbying activities of section 501(c) organizations, see Election Year Issues, Political Campaign and Lobbying Activities of IRC 501(c)(4), (c)(5), and (c)(6) Organizations, and Revenue Ruling 2004-6.
The promotion of social welfare does not include direct or indirect participation or intervention in political campaigns on behalf of or in opposition to any candidate for public office. However, a section 501(c)(4) social welfare organization may engage in some political activities, so long as that is not its primary activity. However, any expenditure it makes for political activities may be subject to tax under section 527(f). For further information regarding political and lobbying activities of section 501(c) organizations, see Election Year Issues, Political Campaign and Lobbying Activities of IRC 501(c)(4), (c)(5), and (c)(6) Organizations, and Revenue Ruling 2004-6.