13 state attorneys general on Thursday filed a brief with the U.S. Supreme Court in the case challenging California’s Proposition 8. (Washington Blade file photo by Michael Key)

Fourteen state attorneys general on Thursday filed a brief with the U.S. Supreme Court in support of marriage rights for same-sex couples.

“Equality under the law is a founding principle of America, but we will not all be equal until everyone has the freedom to choose whom to love and whom to spend their lives with,” Delaware Attorney General Beau Biden said during a news conference in Wilmington. “It is unconstitutional to deny same-sex couples the freedom to marry.”

The brief onto which Connecticut Attorney General George Jepsen, D.C. Attorney General Irvin Nathan, Illinois Attorney General Lisa Madigan, Iowa Attorney General Tom Miller, Maine Attorney General Janet Mills, Massachusetts Attorney General Martha Coakley, New Hampshire Attorney General Michael Delaney, New Mexico Attorney General Gary King, New York Attorney General Eric Schneiderman, Oregon Attorney General Ellen Rosenblum, Vermont Attorney General William Sorrell and Washington Attorney General Robert Ferguson argues California’s voter-approved Proposition 8 denies a variety of legal and social benefits afforded through marriage to same-sex couples and their children. It also highlights nine states and the nation’s capital allow gays and lesbians to marry.

California Attorney General Kamala Harris on Wednesday filed a separate brief with the U.S. Supreme court that urges the justices to strike down Prop 8.

“Our experience in Massachusetts has unequivocally shown that ending the exclusion of same-sex couples from marriage has only strengthened the institution,” Coakley said. “We urge the court to strike Proposition 8 down because it discriminates against gay and lesbian individuals and their families.”

The briefs come ahead of a likely debate on a bill in the Delaware Legislature that would allow gays and lesbians to marry.

An Illinois state House committee on Tuesday approved a same-sex marriage measure, while Minnesota legislators earlier on Thursday introduced a bill that would allow gays and lesbians to marry. Lawmakers in New Jersey and Rhode Island are expected to consider the issue in the coming days and weeks.

“We at Equality Delaware could not be any prouder of our attorney general, Beau Biden, for standing up for freedom and marriage equality for all Delaware families,” Equality Delaware President Lisa Goodman, who spoke at Biden’s news conference, told the Washington Blade.

The state attorneys general filed their brief with the court on the same day Baltimore Ravens linebacker Brendon Ayanbadejo and Chris Kluwe of the Minnesota Vikings again expressed their support for marriage rights for same-sex couples in their own brief that urged the justices to strike down Prop 8.

Equality Virginia, the Utah Pride Center, the Campaign for Southern Equality and other LGBT advocacy groups on Wednesday filed a brief that urges the justices to uphold lower court rulings that found both Prop 8 and DOMA unconstitutional. Former Republican National Committee Chair Ken Mehlman, House Minority Leader Nancy Pelosi (D-Calif.,) Florida Congresswoman Ileana Ros-Lehtinen, gay California Assembly Speaker John Perez and the U.S. Conference of Mayors are among those who have either filed briefs in support of marriage rights for same-sex couples or signed onto them.

Biden and other state attorneys general are expected to file a brief in the DOMA case on Fiday.

The U.S. Supreme Court will hear oral arguments in the two cases on March 26-27.