Will & Grace star Eric McCormack is backing a campaign urging President Barack Obama to support gay marriage.

McCormack is among the celebrities joining Freedom to Marry's Say I Do campaign, which launched Monday with a letter to Obama asking the president for clarity on the topic.

Also joining the campaign are actors Martin Sheen, Lily Tomlin, Jane Wagner and Portia DeGeneres, musicians Melissa Etheridge, Mya and Rufus Wainwright, playwright Tony Kusher and studio executive David Geffen. Also included are social media titans Jack Dorsey, creator of Twitter, and Chris Hughes, co-creator of Facebook, and NFL athletes Brendon Ayanbadejo of the Baltimore Ravens and Scott Fujita of the Cleveland Browns.

McCormack asked Freedom to Marry supporters to add their names to the letter.

“I deeply love my wife Janet, and Finnigan, our eight-year-old son, means everything to us,” McCormack wrote in an email on Monday. “I simply want all of us to be able to marry the person that we love. It's really as simple as that. Whether gay or straight, we all need to stand together as one. Join me by signing Freedom to Marry's letter to President Obama.”

The letter reads: “In law, in love, in life, marriage says 'we are family' in a way that nothing else does. Marriage is the coming together of two lives, marked by a public promise of love and responsibility in front of friends and family. And marriage brings not only public respect and personal significance, but also a safety net of legal protections, rights, and responsibilities for which there is no substitute.”

Obama has said he personally supports government recognition of gay unions but not marriage, a position he recently said he “wrestles” with.