Demonstrators gather outside the Supreme Court in 2013 for a decision on campaign finance rules. (Susan Walsh/AP)

Political nonprofit groups must publicly disclose the names of donors who have given more than $200 toward advertisements or other initiatives that call for the election or defeat of a candidate, according to new guidance from the Federal Election Commission.

In the past, only donors who earmarked their contributions for specific ads needed to be disclosed. Under the new guidance, issued Thursday, donors who give money to the nonprofits — called “dark money” groups by critics — for the more general purpose of independent political activity must now be disclosed.

The guidance was issued in response to a court ruling that expanded the disclosure requirements. That meant the FEC needed to come up with new rules to determine which contributors’ information must be disclosed to the public.

The rulemaking process will take several months, which complicates matters for groups that are now in the heat of political advertising season with just weeks left until the midterm elections. The guidance was issued in the meantime.

Members of the public will get their first look at the newly available information beginning Oct. 15, when it is released by the FEC. Going forward, the FEC will release the information quarterly.

The FEC said the change applies to donors who gave money after Aug. 3, the date of the district court ruling that prompted the change, and for independent political activity that took place after Sept. 18, the date the district court’s ruling went into effect.

While critics of undisclosed political donations hailed the ruling as a step toward greater donor transparency, the FEC guidance indicates that donor disclosure requirements will still be applied to only a subset of donors to such nonprofits.

Supporters of more financial transparency in politics said the directive leaves room for groups to circumvent disclosure.

Paul S. Ryan, vice president of policy and litigation at Common Cause, a group that advocates for greater disclosure in campaign finance, said the wording of the new guidance would allow groups to evade the new requirements by adjusting language on their political ads so that they would not trigger disclosure.

“Zooming out to 30,000 feet, I doubt the new broader donor disclosure standard will have any impact on big independent spenders,” Ryan said. “There’s an easy end run around these new broader disclosure requirements, and big spenders will undoubtedly take advantage in order to lawfully evade donor disclosure.”

Correction: An earlier version of this story suggested the rulemaking process has been completed. It is still ongoing, and the story has been corrected.