On the evening of September 28, the Libertarian and Green Parties, and their 2012 national tickets, filed a federal lawsuit against the Commission on Presidential Debates. The case is Johnson v Commission on Presidential Debates, 1:15cv-1580. It has not yet been assigned to a judge. It asks for a jury trial. It argues that the Sherman and Clayton Anti-Trust Laws do not permit the Commission to hold presidential debates and to exclude all candidates except the Democratic and Republican nominees. The lawsuit asks for damages relating back to the 2012 debates.

The Washington Times has this story about the lawsuit.

UPDATE: the case was assigned to Judge Rosemary Collyer, a George W. Bush appointee. Collyer was appointed by U.S. Supreme Court Chief Justice John Roberts to the U.S. Foreign Intelligence Surveillance Court in 2013; she serves on that court until 2020. Earlier this month she ruled that a lawsuit filed by Republican congressmembers against Obamacare may go ahead.