NOM, co-founded by syndicated columnist Maggie Gallagher, is a non-profit organization that describes its mission as "protect(ing) marriage and the faith communities that sustain it."
From the NOM web site:
Founded in 2007 in response to the growing need for an organized opposition to same-sex marriage in state legislatures, NOM serves as a national resource for marriage-related initiatives at the state and local level. For decades, pro-family organizations have educated the public about the importance of marriage and the family, but have lacked the organized, national presence needed to impact state and local politics in a coordinated and sustained fashion. NOM seeks to fill that void, organizing as a 501(c)(4) nonprofit organization, giving it the flexibility to lobby and support marriage initiatives across the nation.
Marinelli, not exactly a friend of the LGBT community in the past, resigned from NOM a few days ago with an online flourish, writing a blog post called I now support full marriage equality, complete with a retraction of previous negative statements he'd made about gays and lesbians.