The brief, filed with the U.S. District Court for the Eastern District of California, contends that Proposition 8 supporters do not meet the criteria for the limited exemption to valid campaign disclosure laws - an exemption developed by the Supreme Court to protect the ability of historically persecuted minority parties to engage in political speech.

The brief notes that supporters of Proposition 8 are a well-financed association of individuals who raised nearly $30 million in support of a ballot measure that received 52.3 percent of the vote.

" There is no risk that disclosure of donors will harm their ability to organize or otherwise pursue their political views," Brown said.

"Additionally, there is no justification to shield donors from post-election reporting requirements. Rather, these requirements help to prevent kickbacks, laundering, and other improper uses of campaign funds."