'Mayors for the Freedom to Marry' (Blade photo by Michael Key)

A coalition of more than 80 mayors officially kicked off on Friday a campaign to voice their support for same-sex marriage.

Around 15 members of the coalition, known as “Mayors for the Freedom to Marry,” spoke at a news conference at the Capital Hilton during the 80th Winter Meeting of the U.S. Conference of Mayors about the importance of allowing gay couples to marry.

New York City Mayor Michael Bloomberg, an Independent whose state last year legalized same-sex marriage, was among those touting same-sex marriage and said it should be valued by all Americans regardless of their political affiliation.

“Liberals have always opposed discrimination against group identity, and conservatives have always cherished individual freedoms and strong family values,” Bloomberg said. “So marriage equality is consistent with both philosophies.”

According to Bloomberg, 700 gay couples marry at the city clerks offices in New York City each month.

Asked by ABC News whether President Obama, who doesn’t support same-sex marriage, should be aggressive in pressing for gay nuptials, Bloomberg replied, “I would welcome the president to speak out on this. I welcome every member of Congress to speak on this. I’m happy to say that in New York, our senators and most of the congressmen, or many of them, have spoken out already.”

Mayors who sign the pledge, which was written by the group Freedom to Marry, affirm they support same-sex marriage because it improves economic competitiveness and the lives of families in their cities.

“Studies have shown what I know through our hand-on experience — that cities that celebrate and cultivate diversity are the places where creativity and ideas there,” the pledge states. “They are the places where today’s entrepreneurs are most likely to choose to build the businesses of tomorrow. Allowing same-sex couples the right to marry enhances our ability to build this kind of environment, which is good for all of us.”

Mayors of the four largest cities signed the pledge as well as city leaders from states throughout the country identifying Democrats, Republicans and Independents.

Mayor Annise Parker (Blade photo by Michael Key)

Houston Mayor Annise Parker, who two years ago became the first openly lesbian mayor of a major U.S. city, talked about her own life experience as a reason for why same-sex marriage should be legalized.

Parker said she and her partner, Kathy Hubbard, on Monday celebrated their 21st anniversary. She also noted her 35-year-old son, whom she said was 16 and living on the Houston streets when they adopted him because he had been thrown by his family. Parker also said her two adopted daughters, who are now 16 and 21, had previously spent five years in foster care “with very few prospects of a loving, stable home.”

“We had to navigate insurance challenges and custody challenges in the school districts,” Parker said. “One simple thing would have made tremendous difference in the lives of my family and, truly, the lives of millions of Americans, and that is access to the rights and privileges of marriage.”

San Diego Mayor Jerry Sanders, a Republican, was also among those who appeared at the news conference to voice his support from marriage.

In 2007, Sanders made headlines when he reversed his position on marriage equality before signing a City Council resolution intended to overturn the city’s ban on same-sex marriage. The mayor gave a tearful speech in which he said he couldn’t tell his daughter Lisa that her same-sex relationship wasn’t as important as that of straight couple.

During the news conference, Sanders said he “was wrong” about his earlier opposition to same-sex marriage.

“Fairness means giving people the same rights and treating them the same as everyone else,” Sanders said. “There’s no such thing as fair enough; it’s either fair, or it’s not.”

Los Angeles Mayor Villaraigosa said advocating for same-sex marriage is important because he’s seen the harm that measures like Proposition 8 and the Defense of Marriage Act cause for families.

“I’ve often said in L.A. that it doesn’t matter who your father is,” Villaraigosa said. “In my case, it didn’t matter that I didn’t have one. And hopefully soon, it won’t matter if you have two of them. Because if we truly believe in family values, then we should value all of our families.”