Supporters of gay marriage are calling on the Democratic National Committee (DNC) to add marriage equality to the party's 2012 platform.

On Monday, Freedom to Marry launched the Democrats: Say I Do campaign.

“An overwhelming majority of Democrats support the freedom to marry, as do a significant majority of Independents and voters under 50 across the political spectrum,” said Evan Wolfson, founder and president of Freedom to Marry. “The Democratic Party has a noble history of fighting for the human and civil rights of all Americans. It's now time for the national party to be true to its values and its voters and go unequivocally on the record for the freedom to marry.”

(Related: Evan Wolfson, Brian Brown debate gay marriage.)

Freedom to Marry's proposed language also includes support for repealing the Defense of Marriage Act (DOMA), the law that bars federal agencies from recognizing the legal marriages of gay couples, and opposition to constitutional amendments defining marriage as a heterosexual union.

Voters in two states – North Carolina and Minnesota – will decide on such amendments this year.

The DNC will ratify this year's platform during its national convention, which begins September 3 in Charlotte, North Carolina.

A Gallup survey from last year found that 69 percent of Democrats and 59 percent of independents support gay marriage.