Members of the clergy prayed before going into a news conference by the Maryland Marriage Alliance, an organization that includes some Catholic leaders, last week in Annapolis. (Mark Gail/The Washington Post)

The House of Delegates on Friday narrowly approved a bill that would legalize same-sex marriage. The Senate, which passed a similar measure last year, could send the legislation to Gov. Martin O’Malley (D) by the end of the week.

Kathy Dempsey, a spokeswoman for the Maryland Catholic Conference, which is coordinating Monday night’s lobbying efforts, said church leaders and members will thank delegates who voted against the bill and urge senators to oppose it.

And, Dempsey said, “we’re getting ready, if we need to be, for the referendum.”

The Maryland Constitution allows voters to petition just-passed laws to the ballot before they take effect if enough signatures are collected.

The date for the annual Catholic lobbying night was set long ago, and the House moved more quickly on the bill this year than most expected.

After clearing the Senate last year, same-sex marriage died on the House floor. This year, with O'Malley as a sponsor, the bill passed with the help of some late-breaking supporters.

The Catholic Conference has several other issues on its agenda this year.

“Lobby Night is an advocacy event that gives Catholic voters the opportunity to speak in person with their elected officials about issues including abortion clinic regulations, support for pregnant women, poverty, immigration, Catholic schools, the death penalty and marriage,” reads a promotion on the group’s Web site.