Dark money groups will be required to disclose the identities of some anonymous donors after the U.S. Supreme Court on Tuesday refused to stop a lower court’s ruling from taking effect.

Crossroads GPS, a nonprofit Republican group at the center of the case, had asked the high court to put a decision on hold while the case is appealed, but the justices declined.

The ruling in August by the U.S. District Court for the District of Columbia applies to nonprofits that give money to super PACs for advertising that supports or opposes a specific federal candidate, called an “independent expenditure.” Now donors giving more than $200 to nonprofits “for the purpose of furthering an independent expenditure” have to be disclosed to the Federal Election Commission.

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The FEC, which is also a defendant in the case, says the ruling went into effect Tuesday. A Crossroads GPS spokesman didn’t respond to a request for comment.

The case was initially brought by Citizens for Responsibility and Ethics in Washington. The group sued the FEC in 2016, arguing that the agency improperly allowed Crossroads GPS to avoid disclosing donors who had given millions for ads in an Ohio congressional race.

Ellen L. Weintraub, a Democratic FEC commissioner, tweeted that the Supreme Court’s decision was “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,” she said.

Megan McAllen, senior counsel for the nonpartisan Campaign Legal Center, agreed but noted the case is up for appeal.

“This is not the last we’ll see of this,” she said.