A federal appeals court ruled Tuesday that the conservative nonprofit group Americans for Prosperity Foundation, founded by billionaires Charles and David Koch, must disclose its donor list to California law enforcement.

In 2016, U.S. District Court Judge Manuel Real issued a permanent injunction against the state's rule requiring that the nonprofit file its list of donors. Americans for Prosperity argued that it was a violation of the First Amendment. Disclosing the list, they contended, would dissuade potential and current donors from giving, and it would expose donors to threats and harassment.

The three-person panel of the U.S. 9th Circuit Court of Appeals in San Francisco unanimously reversed the injunction. In a 41-page opinion written by Judge Raymond Fisher and joined by Judges Richard Paez and Jacqueline Nguyen, Fisher argues that, "The mere possibility that some contributors may choose to withhold their support does not establish a substantial burden on First Amendment rights." The group failed to show that there would be a significant burden on donors if the state had access to the list.

The state rarely uses this information that's already collected by the Internal Revenue Service, and the chances of the donor list accidentally getting released, the court said, is "slight." California, the court noted, would only use the information to prevent charitable fraud, and the information would not be released to the public "except in very limited circumstances."

Fisher, however, said that it was true that some people connected to the Americans for Prosperity Foundation had been subjected to threats, and the court said it had "serious concerns" about lapses that lead to disclosure of the donor list in the past when the charity filed its public taxes.

The court said it was unclear whether the threats resulted from ties to the foundation or for other reasons. Fisher also wrote in the opinion that, "Nothing is perfectly secure on the internet in 2018, and the Attorney General’s data are no exception, but this factor alone does not establish a significant risk of public disclosure."

The state, the court assured in the opinion, has taken steps to prevent this kind of leak in the future.

Tim Phillips, the head of Americans for Prosperity, testified to the court saying that he believes the nonprofit is being targeted for political reasons. Democratic Sen. Kamala Harris was the attorney general of California when the litigation started, and Democrat Xavier Becerra, a former House member, is overseeing the case now.

This ruling comes after the Koch political network announced Monday that they would launch a super PAC called Americans for Prosperity Action ahead of the 2018 midterm elections. The super PAC would support candidates or issues related to the objectives of the Americans for Prosperity Foundation. In January, the Kochs pledged to donate almost $400 million into the November elections.

The Michigan-based, conservative Thomas More Law Center pursued a similar case as Americans for Prosperity in California, and the challenge was also rejected on Tuesday.

Americans for Prosperity and the Thomas More Law Center could ask for a larger review of their cases by an 11-judge court, or they could take their cases to the Supreme Court.