If it believes there is a conflict, the Justice Department, as a party to the case, should ask the court to reconsider its decision, Common Cause said.
The landmark case, Citizens United vs. Federal Election Commission, was decided a year ago this week. It permitted corporate and union funds to be spent directly on election advertising, a practice that had previously been restricted. The Kochs have been significant donors to independent-expenditure campaigns, which increased dramatically after the Citizens United decision.
The letter is based in part on references to Scalia and Thomas made in an invitation to an upcoming meeting this month of elite conservative leaders sponsored by the Kochs. The invitation, first obtained by the liberal blog Think Progress, names the two justices among luminaries who have attended the closed Koch meetings at unspecified dates in the past.
Representatives of the Kochs declined repeated requests for comment. The Justice Department did not immediately respond to a request for comment. Decisions about recusal from individual cases are up to each individual justice.
Some legal scholars dismiss the complaint as unlikely to succeed. But others said raising the issue could engender useful public scrutiny and debate about judicial independence.
Steven Gillers, a legal ethics specialist at New York University, said the Koch brothers' use of Scalia and Thomas' name for their upcoming meeting was "troubling."
"I believe the nation has a right to know exactly what role if any the Justices played in the Koch gatherings, including the content of any remarks they made and whether Citizens United was a subject of any gathering they attended," Gillers said. "The answers can help determine whether they were able to sit in the case and, if not, whether the result should be overturned.
In the invitation letter to a meeting later this month in Palm Springs, Calif., sent on Koch Industries stationery, Charles G. Koch encourages attendance, saying that "twice a year our network meets to review strategies for combating the multitude of public policies that threaten to destroy America as we know it."
Supreme Court spokesperson Kathy Arberg said that Justices Thomas and Scalia had traveled to Indian Wells, California, to address a Federalist Society dinner sponsored by Charles and Elizabeth Koch but did not actively participate in the separate Koch strategy and policy meetings. Justice Scalia spoke about international law at the January 2007 meeting of the quasi-academic Federalist Society and did not attend the separate political and strategy meeting hosted by the Kochs, she said. Justice Thomas spoke to the Federalists at the same location in January 2008 about his recently published book. Thomas then dropped by one of the separate Koch meeting sessions. "It was a brief drop by," Arberg said. "He was not a participant."
It is common for members of the federal judiciary to attend events where legal and political issues are discussed. But the law prohibits them from taking part in cases where their impartiality might reasonable be questioned. In their letter to Holder, Common Cause executives say that such a conflict appears to exist.