WASHINGTON (CNN) - A Supreme Court move on Tuesday could mean that so-called "dark money" groups would have to disclose the names of their donors, potentially chipping away at a longstanding shroud of secrecy surrounding money in politics.
The move also creates uncertainty around those groups' efforts to raise and spend money just seven weeks from the midterm elections.
The court let stand a federal judge's decision to throw out a decades-old Federal Election Commission regulation that only required nonprofit groups to name their donors when their contributions were earmarked for specific advertisements.
The ruling was a blow to Crossroads GPS, the conservative nonprofit linked to Republican strategist Karl Rove that was involved in the case and had sought the emergency stay. It means nonprofit groups like Crossroads GPS could face new requirements to reveal their donors before November's midterm elections. Crossroads GPS is the No. 2 "dark money" spender since the 2010 Citizens United vs. FEC ruling, according to a recent report by the nonprofit campaign finance group Issue One.
FEC Chairwoman Caroline Hunter told The Washington Post that the names of donors who give money to nonprofits to be used in political campaigns beginning Wednesday will have to be reported. Hunter did not respond to CNN's request for comment.
However, Judge Beryl Howell's August ruling appears to leave avenues for the groups to raise money without disclosing donors -- such as making vague solicitations that aren't linked to attempts to elect or defeat specific candidates, or avoiding "express advocacy," to instead spend money on issue ads that still aim to steer voters.
There are other loopholes -- particularly for nonprofit groups that don't advocate for candidates themselves, but send money to super PACs that do -- that can also help shield the identities of groups' donors.
The FEC could soon answer questions about how the ruling will be implemented.
"This is a real victory for transparency. As a result, the American people will be better informed about who's paying for the ads they're seeing this election season," tweeted Democratic FEC commissioner Ellen Weintraub.
Advocates for stronger donor disclosure requirements in politics, including the Citizens for Responsibility and Ethics in Washington, which challenged the decades-old FEC rule that the federal judge threw out, celebrated the decision.
"This is a great day for transparency and democracy," CREW Executive Director Noah Bookbinder said. "Three courts, including the Supreme Court, have now rejected Crossroads' arguments for a stay, meaning we're about to know a lot more about who is funding our elections."
Crossroads GPS spokesman Chris Pack said the group will comply with the law.
"While we are disappointed the Supreme Court did not take this opportunity to ensure regulatory clarity for nonpolitical organizations that lawfully engage in election activity," Pack said, "we are confident we can navigate through the current morass and comply with the law, as we always have."
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