Public Citizen assisted in representing then-U.S. Rep. Chris Van Hollen in challenging the FEC’s failure to require organizations that spend money on electioneering communications to disclose the identities of all contributors who donate $1,000 or more, as required by the McCain-Feingold Act. Instead, the FEC required disclosure only of donors who specifically earmarked contributions for specific ads. The district court initially ruled in Van Hollen’s favor on the ground that the FEC’s regulation violated unambiguous statutory requirements. Organizations opposing disclosure appealed, and the D.C. Circuit reversed the district court’s plain language ruling and remanded for a determination of whether the FEC’s construction of the statute was reasonable. The district court granted Van Hollen’s motion for summary judgment, and although the FEC declined to appeal that ruling, the intervening organizations who opposed disclosure appealed. The D.C. Circuit again reversed, holding that the FEC’s regulation merited Chevron deference and was not arbitrary and capricious.