The group was confronted by church members but only left after the police were called, before re-forming on the pavement outside the church.
Pastor Elijah Zehyoue of Calvary said the protesters were "aggressively engaging" members arriving for the 11am service, as well as a passer-by who appeared to be interested in attending the church.
The protesters, who said Calvary members were "going to hell" and that the church was "the house of Satan", reportedly did not identify themselves as representing any particular group.
The protest came after the church announced on 9 January that it was hiring Sally Sarratt and Maria Swearingen as the congregation's new senior ministers.
The couple, who married the weekend after same-sex marriage became legal in South Carolina (SC) in 2014, were ordained to the ministry by First Baptist Church in Greenville, SC, the following year.
The women, who are currently chaplains in the Greenville area, are scheduled to begin their work at Calvary on 26 February.
Zehyoue said of the protesters: "It was pretty difficult to get them to stop and leave the sanctuary. Outside they were still pretty aggressive with members and visitors and a random passer-by who looked like they may have been coming to the church."
The church was almost empty when the protesters took over the pulpit, except for choir members who were practicing at the time.
Nonetheless, Zehyoue, who is preparing new security measures before the pastors join in February, said the incident was "disturbing and unnerving".
Church moderator Becky Vaughn added: "While the language was not comfortable, it was still basically peaceful. There was no effort to do harm, and they did move out to the side-walk."
She said that about 15 members stayed at the front door while the protesters remained on the pavement, adding that members prayed and sang hymns and "assured them that God loves them and we love them."
After the confrontation the morning service went ahead planned, with the associate pastor, Erica Lea preaching her scheduled sermon: a call to unity.
"As disturbing as it was, the protest was a good moment where many of our church members were energised and found the presence of the Holy Spirit on the steps of our church and that was powerful moment," said Zehyoue.
He added that it was "what we call just another Sunday at Calvary."