The legal group said that for those associated with charities like the Thomas More Law Center that "speak on contentious matters," the disclosure of donor information "poses an imminent danger of hate mail, violence, ostracization, and boycotts."
"Only the most stalwart supporters will give money under such a toxic cloud. Most will reasonably conclude that the risk of association is too great, with the result that groups who make the most threats will effectively shut down those with whom they disagree," said the legal group's request for Supreme Court review.
"Charities will continue to find as-applied exemptions impossible to achieve, and support for groups advocating contentious ideas will dry up," the legal group said. "This Court should intervene now while there are still dissenting voices left to save."
The request said California law has "deprived charities of resources, chilled their speech for nine years, and blocked dissemination of their ideas in our Nation's most populous state."
Alliance Defending Freedom has cited the Supreme Court's 1958 ruling in the case NAACP v. Alabama, which ruled against the Alabama Attorney General's demands that the civil rights group produce its membership list or cease operations. The restrictions on the group crippled the organization in Alabama at a key time when black Americans sought to secure civil rights.
The NAACP Legal Defense and Education Fund filed a friend-of-the-court brief on behalf of the Americans for Prosperity Foundation.
The district court found that California's required disclosures were not "substantially related" to its interest in regulating charities, as auditors and attorneys seldom use the Schedule B section when they audit or investigate charities. Even when the information was relevant, it could be obtained from other sources. The disclosure requirement was not narrowly tailored.
The district court said petitioners presented "ample evidence" that their contributors had previously suffered "harassment, reprisals, and similar harms" when their involvement became known. The California attorney general's office had "systematically failed to maintain the confidentiality of Schedule B forms." This failure included making hundreds of the forms available on its registry website.
The court of appeals, however, overturned the district court. It said confidentiality measures had been tightened and said California had a compelling interest in policing fraud in charitable organizations, and disclosing major donors advances this interest, Reuters reported.
It compared the rule to political disclosure cases such as Doe v. Reed, where the Supreme Court said that the disclosure of the names of people who signed a petition referendum was relevant to state interests in protecting the electoral process.
Alliance Defending Freedom's summary of the case said, "the California Attorney General's office has a history of posting supporter's information online and offers no protection against employees, contractors, or summer interns downloading, e-mailing, or printing supporters' names and addresses and then disclosing them publicly."
"We've already seen how publicly revealing political donors with the intent of doing harm (or 'doxing') can ruin careers and corrode civil discourse," the legal group said. "Givers would have good reason to fear being doxed-especially in today's toxic cultural climate."
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The Thomas More Law Center's president and chief counsel is Richard Thompson, who came to prominence for opposing prominent assisted suicide advocate Jack Kevorkian. Thompson co-founded the law center in in 1998 with Thomas Monaghan, the founder of Domino's Pizza who continues to be a prominent Catholic philanthropist. Alliance Defending Freedom said about 5% of donors to the law center are California residents.
Besides issues related to religious freedom and family values, the law center's website also provides resources for critics of the Common Core curriculum. It names other key issues as "confronting the threat of radical Islam" and "defending national security."
The similarly-named Thomas More Society, based in Illinois, is not connected to the law center.
For its part, Americans for Prosperity was founded in 2004. It has had strong financial support from two wealthy brothers, David and Charles Koch, whose combined net worth is in the billions of dollars.