Rev. Nancy Ellett Allison has joyfully officiated same-sex marriages in her corner of the conservative South since 2006.

“It is just a delight to be able to help these couples celebrate their lives together and work with them to craft their vows,” said Allison, her bright voice laced with a twang.

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What Allison, the senior pastor at Holy Covenant United Church of Christ in Charlotte, N.C., has been doing is considered a misdemeanor crime under state law, punishable by up to 120 days in jail. Not only are gay marriages and domestic unions illegal in the state, but it’s considered criminal for clergy to officiate religious vows for couples who have not yet obtained a valid marriage license.

This week, though, the progressive United Church of Christ fought back, filing the first federal lawsuit to say gay marriage bans are a violation of religious rights. It’s an unprecedented move; experts say it’s the first such lawsuit ever in the United States.

The church joined with plaintiffs that include Allison, other UCC ministers, and six same-sex couples to file a lawsuit Monday against North Carolina state and county officials challenging the constitutionality of the state’s antigay marriage laws as violating the church’s free exercise of religion. In 2012, voters approved a ballot measure to ban gay marriage, imposing a legal definition of marriage as an act that can occur only between a man and a woman, and making it part of the state’s constitution.

The UCC’s lawsuit seeks a preliminary and permanent injunction against all laws that would make it a crime to perform religious rites that sanctify the union of same-sex couples.

“Not until we entered this lawsuit was I aware that it was illegal to perform a same-gender marriage ceremony without a marriage license. That was one of the shocking things I learned,” said Allison, who noted that Charlotte, like other major North Carolina cities, is more open-minded than rural areas, and that the state voted for President Barack Obama in 2008 (though Republican Mitt Romney won it in 2012).

As for reactions to the lawsuit from the conservative Christians in the faith community, Allison said she was surprised by a podcast by fundamentalist antigay marriage religious leader Albert Mohler Jr., president of the Southern Baptist Theological Seminary in Louisville, Ky. Though he opposes the UCC’s liberal views, he voiced his concerns over threatened religious freedoms. Allison was originally ordained in 1981 in the Southern Baptist Church in Dallas before joining the United Church of Christ.

“He said our freedom to preach heresy should be protected,” she said. “From my perspective, he is preaching heresy. From his perspective, I am. I do think it’s just a matter of time that these marriage laws will change.”

Religious freedom and its basis as a First Amendment right are a prime issue at the center of the lawsuit, as is sheer antigay bias. The government has to have secular reasons for imposing laws and can’t pick on a religious practice, said attorney Jennifer Pizer, senior counsel at gay rights organization Lambda Legal.

However, a precedent has been set with our neighbors to the north.

“This is the first case of its kind in the U.S. but not in the world,” Pizer said. In 2001, Canada’s Metropolitan Community Church won a lawsuit validating same-sex marriages conducted and registered by clergy across Ontario.

As for a backlash against the lawsuit, Allison said she and her congregation were taking preventive measures. A congregation member and former police officer arranged to have an officer on duty at this Sunday’s church service, she said. Also, if someone tries to interrupt, the church’s pianist plans to launch into a rousing version of “Amazing Grace” to get parishioners standing up and singing.

In the meantime, will Allison stop officiating same-sex marriages?

“Nope,” she declared. She’s prepping for the October wedding of lawsuit plaintiffs Kathleen Smith and Lisa Cloninger.

“They’ve already sent out save-the-date cards and bought their dresses,” Allison said. “They’re going to get married in a religious ceremony in October, and nothing would please us more than if they could get married legally at that time.”