Ellen Barkin has joined the cast of a new play based on the trial over the constitutionality of California's gay marriage ban, Proposition 8.

The 13-day trial, held last year in San Francisco, resulted in federal Judge Vaughn Walker, now retired, declaring the 2008 voter-approved amendment unconstitutional. Proponents of the ban appealed the ruling, and gay and lesbian couples in California remain barred from marrying.

Milk scribe Dustin Lance Black penned the play, which is simply titled 8 and is based on trial transcripts and interviews. Black told The New York Times that the play was six months in the making.

“I mined the best arguments on both sides, trying to capture everything on their side that was a winning point and anything on our side that was a winning point,” he said.

Barkin will play Sandy Stier, who along with her partner of eleven years, Kris Perry (played by Christine Lahti), make up one of the two gay couples suing the state for the right to marry.

Matt Bomer and Cheyenne Jackson will play Jeff Zarrillo and Paul Katami, the second couple.

Bob Balaban will play Judge Walker, while Morgan Freeman and John Lithgow will play David Boies and Theodore B. Olson, the two attorneys arguing for the plaintiffs.

Monday's one-time staged reading at Broadway's Eugene O'Neil Theatre will benefit The American Foundation for Equal Rights, the group formed specifically to challenge Proposition 8.

Subsequent productions are planned at Carnegie Mellon University, Northwest, and the University of Michigan.

Tickets begin at $500.