Most of the funding for the National Organization for Marriage, a 501(c)(4) “grassroots” group dedicated to opposing same-sex marriage in Florida and elsewhere, comes from a few sources, according to its most recent 2009 IRS 990 form.

“The National Organization for Marriage has emerged as the nation’s only major national grassroots organization dedicated to protecting marriage,” said the organization’s president and founder, Maggie Gallagher, in July 2009. The group describes itself as “the nation’s only grassroots organization focused on the threat to marriage at state and local levels.” Executive Director Brian Brown said in a January 2010 press release, “NOM’s goal is a national grassroots organization that can make a difference in all 50 states, as needed.”

However, at least in terms of funding, its donations are quite concentrated. According to its 2009 990 forms (.pdf) obtained by the Human Rights Campaign, the National Organization for Marriage received $7,106,388 in donations in 2009. Three donations of $2.4 million, $1.2 million, and $1.1 million constituted 68 percent of its total donations. Two additional donations of $400,000 and $150,000 mean that three-quarters of its funding came from just five sources.

Donations to 501(c)(4) organizations are not tax-deductible, and organizations do not have to disclose their donors.

Writing for The Washington Independent, Jesse Zwick uncovered a $1.4 million donation from the Knights of Columbus to the National Organization for Marriage in 2009, which does not seem to appear on the organization’s 990. The group has a pattern of pushing the boundaries of disclosure laws: The organization sued the Rhode Island Board of Elections over the funding of ads, has been the subject of campaign finance complaints in Maine and Iowa, and used a loophole in Minnesota campaign finance law, all to avoid disclosure.

A request for comment to the National Organization For Marriage was not immediately returned.

(Full disclosure: The American Independent News Network is a 501(c)(3) organization. Our donors can be viewed here.)

Luke Johnson reports for The American Independent.