Maryland Gov. Martin O'Malley at the March 1 signing of the state’s same-sex marriage law. (Photo by Linda Davidson/The Washington Post)

The money was tied to a fundraiser held in the Chevy Chase home of Susie and Michael Gelman, both of whom have long been active in Democratic politics and are supporters of Gov. Martin O’Malley (D).

O’Malley was billed as the “honored guest” at the event, which about 70 people attended, said Kevin Nix, a spokesman for Marylanders for Marriage Equality, the group coordinating the campaign to uphold the law.

If it is upheld, Maryland would become the first state in the country — or at least among the first — to grant same-sex marriage rights in a statewide vote. Similar measures are on the November ballot in Maine and Washington state.

Maryland’s law, which O’Malley signed in March, was successfully petitioned to the ballot by same-sex marriage opponents. The law is scheduled to take effect in January, pending the outcome of the vote.

The minimum contribution to Wednesday night’s fundraiser was $500 per person. Many guests gave $5,000, $10,000 or more, according to organizers. There is no limit in Maryland on contributions to ballot-issue committees.

Michael Gelman, the event’s host, is founder of an accounting firm. Both Gelmans have also been active in the Jewish community and donated money to Democrats at all levels of politics.

Besides O’Malley, other politicians at the event included Lt. Gov. Anthony G. Brown, who is among the Democrats seeking to succeed O’Malley in 2014; and Sen. Richard S. Madaleno Jr. (D-Montgomery), one of eight openly gay members of the General Assembly.

Madaleno, who attended with his husband, Mark Madaleno Hodge, credited O’Malley with giving “one of his best, most moving speeches” on the issue of same-sex marriage.