Cook County Circuit Judge Sophia Hall is presiding over a lawsuit filed by 25 gay and lesbian couples who want to overturn the 16-year-old law.
But Cook County State's Attorney Anita Alvarez and Attorney General Lisa Madigan refused to defend it, saying the ban violates the constitution.
Two downstate Illinois county clerks already received permission to defend the law. Now the institute and the Arlington Heights-based Church of Christian Liberty and Bensenville-based Grace Gospel Fellowship say they should be able to intervene, too.
The American Civil Liberties Union and Lambda Legal are representing the plaintiffs. They say there's no legal reason for more groups to intervene.
