Caroline Kennedy on Monday endorsed adding gay marriage to the 2012 Democratic platform.

Freedom to Marry announced that Kennedy had joined its Democrats: Say I Do campaign, which calls for adding marriage equality to this year's platform.

“There are few things in life more important than being able to marry and build a family with the person you love. This fundamental right should be available to all Americans, including gay and lesbian couples,” Kennedy is quoted as saying. “In our democracy we are fortunate to have elected officials at all levels of government, and courageous jurists who have put their careers on the line, to uphold the promise of equality that is as old as our Constitution, and I hope that many more will follow their example.”

“Freedom to Marry is proud that Caroline Kennedy has joined the growing chorus of Democratic voices in our call for a freedom to marry plank in the national Democratic Party Platform,” said Evan Wolfson, founder and president of Freedom to Marry.

Democrats who have endorsed putting marriage equality in the platform include Democratic National Convention chair Antonio Villaraigosa, House Minority Leader Nancy Pelosi, U.S. Senate candidate Elizabeth Warren and nearly two dozen U.S. senators.

Nearly 40,000 Democrats have added their names to Freedom to Marry's Democrats: Say I Do online petition.

(Related: Caroline Kennedy urges Obama to support gay marriage.)