Mayors Rahm Emanuel of Chicago, Mike Bloomberg of New York City and Antonio Villaraigosa of Los Angeles are among 80 mayors pledging to support gay marriage.

The group Mayors for the Freedom to Marry launched Friday with a press conference held at the 80th annual U.S. Conference of Mayors in Washington D.C.

“If we truly believe in family values, we should value all families,” said Villaraigosa, president of the U.S. Conference of Mayors and a co-chair of the new group. “Denying gay and lesbian couples the freedom to marry weakens society by hurting our communities, neighbors and families. We hope other mayors will sign the pledge and join Mayors for the Freedom to Marry.”

Mayors involved will lobby state lawmakers to approve marriage equality legislation and call on Congressional representatives to repeal the Defense of Marriage Act (DOMA), which bars federal agencies from recognizing the legal marriages of gay and lesbian couples.

Bloomberg, who strongly backed New York becoming the sixth state to legalize gay marriage, and San Diego Mayor Jerry Sanders also gave remarks.

“In only a season, the freedom to marry has already made New York a stronger state,” Bloomberg said. “This isn't about partisanship or ideology. It's about extending the freedoms of our country to all people, and ensuring equal protection under the law. Mayors understand that welcoming committed gay couples to the rights and responsibilities of marriage isn't just the right thing to do, it's also the smart thing to do for the diverse, dynamic, forward-looking cities we're all working to build.”

Sanders added: “Marriage encourages people to take responsibility for each other, provides greater security for children and helps our country live up to the promises set forth in our founding documents.”

Sanders, a Republican, provided emotional testimony during the second week of the trial that found California's gay marriage ban, Proposition 8, unconstitutional. He testified that he once opposed marriage equality. In 2007, he was prepared to veto a San Diego City Council-approved resolution calling on the city to file an amicus brief in support of a San Francisco legal challenge. Instead, with his wife by his side, Sanders held a tearful press conference and told reporters: “I have close family members and friends who are members of the gay and lesbian community. Those folks include my daughter Lisa.”

Also involved in the campaign are Mayors Annise Parker of Houston and Marilyn Strickland of Tacoma.