The ceremony, which will be largely symbolic because Pennsylvania does not recognize same-sex marriage, is being held in support of the Rev. Frank Schaefer of Lebanon. On Nov. 18, Schaefer is being put on trial by the church for having presided over his son's 2007 marriage to another man.
The Rev. Herb Snyder, a retired minister affiliated with Arch Street, said he had been approached by about a half-dozen clergy from other faiths and denominations - including Judaism, the United Church of Christ, and the Episcopal Church - who would like to take part in the ceremony.
"It's really affirming and encouraging to see firsthand that there are so many people who want an inclusive church and are willing to put their necks out for this," Snyder said.
A conservative coalition of pastors from the church's Eastern Pennsylvania Conference on Thursday called for the group to reconsider its plans, saying clergy have the right to challenge doctrine through available channels but cannot "break those rules unilaterally."
Brown has said it will be more difficult for the church to prosecute following their ceremony because of the large number of officiants. In a news release, the Evangelical Connection of the Eastern Pennsylvania Conference of the United Methodist Church said the pastors were trying to "paralyze" the church's system of accountability and "render our Book of Discipline inoperable."
"We grieve over the potential of this intended action to threaten the very fabric of our unity," the release said.
The names of the men who will take part in the same-sex wedding ceremony have not been released. Brown said they have been together for 25 years and have been members of Arch Street for 20. The ceremony will take place at 3 p.m. at Arch Street.