The NAACP passed a resolution Saturday endorsing same-sex marriage as a civil right and opposing any efforts "to codify discrimination or hatred into the law."
The National Association for the Advancement of Colored People's board voted at a leadership retreat in Miami to back a resolution supporting marriage equality, calling the position consistent with the equal protection provision of the U.S. Constitution.
"The mission of the NAACP has always been to ensure political, social and economic equality of all people," Board Chairwoman Roslyn M. Brock said in a statement. "We have and will oppose efforts to codify discrimination into law."
Same-sex marriage is legal in six states and the District of Columbia, but 31 states have passed amendments to ban it.
The NAACP vote came about two weeks after President Barack Obama announced his support for gay marriage, setting off a flurry of political activity in a number of states. Obama's announcement followed Vice President Joe Biden's declaration in a television interview that he was "absolutely comfortable" with gay couples marrying.
"Civil marriage is a civil right and a matter of civil law. The NAACP's support for marriage equality is deeply rooted in the Fourteenth Amendment of the United States Constitution and equal protection of all people" said NAACP President Benjamin Todd Jealous, a strong backer of gay rights.
Gay marriage has divided the black community, with many religious leaders opposing it. In California, exit polls showed about 70 percent of blacks opposed same-sex marriage in 2008. In Maryland, black religious leaders helped derail a gay marriage bill last year. But state lawmakers passed a gay marriage bill this year.
Pew Research Center polls have found that African Americans have become more supportive of same-sex marriage in recent years, but remain less supportive than other groups. A poll conducted in April showed 39 percent of African-Americans favor gay marriage, compared with 47 percent of whites. The poll showed 49 percent of blacks and 43 percent of whites are opposed.
The Human Rights Campaign, a leading gay rights advocacy group, applauded the step by the Baltimore-based civil rights organization.
"We could not be more pleased with the NAACP's history-making vote today _ which is yet another example of the traction marriage equality continues to gain in every community," HRC President Joe Solmonese said in a statement.