U.S. Supreme Court weighs conservative groups' bid to conceal donors

The U.S. Supreme Court on Monday is set to hear arguments in a challenge by two conservative groups to a California requirement that tax-exempt charities disclose to the state the identity of their top financial donors.

The nonprofit groups - the Americans for Prosperity Foundation and the Thomas More Law Center - argued that California's policy violated the U.S. Constitution's First Amendment guarantees of freedom of speech and association. They argued that if the information were to be made public it could lead to harassment or threats to their donors.

The Thomas More Law Center is a conservative Catholic legal group. The Americans for Prosperity Foundation, which funds education and training on conservative issues, is the sister organization of Americans for Prosperity, a conservative political advocacy group - both founded by conservative billionaire businessman Charles Koch and his late brother David.

Democratic-governed California, the most populous U.S. state, has said the donor information is required from such groups as part of the state attorney general's duty to prevent charitable fraud.

The state requires that charities provide a copy of the tax form they file with the U.S. Internal Revenue Service that lists donors who contribute large amounts. Larger groups have to disclose donors who contribute $200,000 or more in any year. That information is not posted online and is kept confidential.

The Supreme Court, which has a 6-3 conservative majority, is set to hear an appeal by the groups of a lower court decision upholding the policy, which has been in place since 2010.

The two groups are backed in the case by nonprofit organizations across the ideological spectrum including liberal groups such as the American Civil Liberties Union and the Human Rights Campaign, an LGBT rights group, as well as business groups such as the U.S. Chamber of Commerce.