Yesterday, a joint brief was filed by a number of groups, including the Center for Inquiry, Americans for Religious Liberty, and the various members of the Secular Coalition for America (including American Atheists, American Ethical Union, American Humanist Association, the Institute for Humanist Studies, Military Association of Atheists and Freethinkers, Secular Student Alliance, and the Society for Humanistic Judaism).
MORE: http://www.patheos.com/blogs/friendlyatheist/2013/09/25/several-atheist-groups-file-joint-amicus-brief-for-supreme-court-prayer-case/
See also...
U.S. to argue in N.Y. town's prayer at meetings case
http://www.usatoday.com/story/news/nation/2013/09/17/supreme-court-prayer-town-meetings/2827009/
DOJ Disappointment: Obama Administration Wants To Help Religious Right In Supreme Court Prayer Case
https://au.org/blogs/wall-of-separation/doj-disappointment-obama-administration-wants-to-help-religious-right-in
Reason To The Rescue: Members of Congress, Scholars and Faith Leaders Voice Opposition To Coercive Sectarian Prayer Before Local Board Meetings
https://au.org/blogs/wall-of-separation/reason-to-the-rescue-members-of-congress-scholars-and-faith-leaders-voice