Two government lawyers in Illinois are refusing to defend the state's ban on same-sex marriage.
Attorney General Lisa Madigan and Cook County State's Attorney Anita Alvarez say the ban violates the state constitution's equal protection clause.
The decision sets up a scenario where a judge could easily strike down the 16-year-old law.
It could also put Illinois in the national spotlight as federal and state courts wrestle with the gay marriage issue.
Peter Breen, executive director of the Thomas More Society, a non-profit, national public interest law firm, said he was disappointed with Alvares' decision.
"Today's announcement by State's Attorney Alvarez makes it clear that this lawsuit was an 'inside job' from the beginning, a crass political move to force same-sex marriage on all Illinoisans without providing the residents of the other 101 counties an opportunity to be heard," he charged.
Breen made it clear his organization had no intention of taking Alvarez's decision lying down.
"The Thomas More Society is preparing legal papers to defend the law and prevent this collusive end run around the will of the people of Illinois and their General Assembly," he said.