The documentary To a More Perfect Union: United States v. Windsor opens in theaters nationwide June 7.

The film chronicles Edie Windsor's legal battle to have her Canadian marriage to Thea Spyer recognized by the U.S. federal government.

Director Donna Zaccaro's film will screen in more than 20 major cities, including Los Angeles, New York, Chicago, San Francisco, Denver, Atlanta, Austin, Palm Springs, San Diego and Washington, D.C.

Spyer died in 2009, two years after the women married in Canada. Windsor challenged the Defense of Marriage Act (DOMA), which prohibited the federal government from recognizing the couple's marriage, after she received a $363,000 estate tax bill following Spyer's death.

The 2013 Supreme Court ruling that struck down a key provision of DOMA is also credited with providing the legal framework for 2015's landmark ruling in Obergefell, which found that gay couples have a constitutional right to marry.

The film includes interviews with Windsor's attorney Roberta Kaplan, journalists Frank Rich and Nina Totenberg, marriage equality advocate Evan Wolfson and Windsor herself.

Windsor died last year. She was 88.