Derek McCoy, right, executive director of the Maryland Marriage Alliance, lobbied against the gay nuptials bill in Annapolis. (Photo by Mark Gail/The Washington Post)

“The General Assembly and the governor do not have the final word on marriage in Maryland,” said Derek McCoy, executive director of the Maryland Marriage Alliance, the group leading the petition effort. “The people do.”

If opponents gather 55,736 valid signatures from Maryland voters by June 30, the new law will be put on hold pending the outcome of a November ballot measure.

Just about everyone, including Gov. Martin O’Malley (D), who sponsored the same-sex marriage bill, expects the issue to be decided at the polls.

McCoy’s group is directing interested parties to a Web site that facilitates a petition form being mailed to them with their voter registration information pre-filled out. That is meant to cut down on the number of signatures that are later ruled invalid by election officials.

McCoy also pledged “a massive grassroots effort” to sign up voters in their neighborhoods, at shopping centers and at their churches.

The new law, which O’Malley signed two weeks ago, seeks to make Maryland the eighth state, in addition to the District, to allow same-sex marriage.

The bill is scheduled to take effect Jan. 1.

A Washington Post poll in January showed 50 percent of Marylanders supported allowing same-sex marriage, while 44 percent were opposed.

Supporters of the legislation have also started a petition drive, though it has no bearing on the referendum process.