http://www.southernstudies.org/2015/10/nonprofits-that-spent-millions-backing-southern-ca.html
"If the groups are found to have violated the law, the potential penalties from the IRS include revoking their 501c4 status, imposing taxes on them, and treating them as taxable corporations or 527 political organizations, which are required to disclose their donors.
But the chance of enforcement by the IRS is slim. According to the Center for Public Integrity, the agency has "all but [quit] its regulation of politically active nonprofits" after coming under fire from conservative groups whose applications for nonprofit status were delayed in the approval process. In addition, Congress has made significant cuts to the IRS budget, and fewer employees are investigating nonprofits."
