A film that documents the case to overturn Proposition 8, California's now-ended ban on gay marriage, will open in New York and Los Angeles on June 6.

The Case Against 8 won the Directing Prize for U.S. Documentary at the 2014 Sundance Film Festival.

California voters approved Proposition 8 in 2008, sparking massive protests in California and Utah, home to the Mormon Church which played a key role in its passage.

The following year, two plaintiff couples – Kristin Perry and Sandy Stier and Paul Katami and Jeff Zarillo – challenged the amendment's constitutionally. It was the first case to aim for the Supreme Court.

The film's June 6 release date coincides with the first anniversary of the Supreme Court's landmark ruling in the case. The documentary will expand to selected cities June 13.

The Case Against 8, directed by Ben Cotner and Ryan White, premiers Monday, June 23 on HBO.