Although there have been suits against wedding industry businesses that refuse to serve gay couples, attorneys promoting the bylaw changes say they don't know of any lawsuits against churches.
Critics say the changes are unnecessary, but some churches fear that it's only a matter of time before one of them is sued.
"I thought marriage was always between one man and one woman, but the Supreme Court in a 5-4 decision said no," said Gregory S. Erwin, an attorney for the Louisiana Baptist Convention, an association of Southern Baptist churches and one several groups advising churches to change their bylaws. "I think it's better to be prepared because the law is changing. America is changing."
In a June decision, the U.S. Supreme Court struck down a provision of the federal Defense of Marriage Act that defined marriage as between a man and a woman for purposes of federal law. A second decision was more technical but essentially ushered in legal gay marriage in California.
Kevin Snider is an attorney with the Pacific Justice Institute, a nonprofit legal defense group that specializes in conservative Christian issues. His organization released a model marriage policy a few years ago in response to a statewide gay marriage fight in California. Snider said some religious leaders have been threatened with lawsuits for declining to perform same-sex wedding ceremonies.
Dean Inserra, head pastor of the 1,000-member City Church Tallahassee, based in Florida, said he does not want to be alarmist, but his church is looking into how best to address the issue.
Inserra said he already has had to say no to gay friends who wanted him to perform a wedding ceremony.
"We have some gay couples that attend our church. What happens when they ask us to do their wedding?" Inserra said. "What happens when we say no? Is it going to be treated like a civil rights thing?"
Critics, including some gay Christian leaders, argue that the changes amount to a solution looking for a problem.
"They seem to be under the impression that there is this huge movement with the goal of forcing them to perform ceremonies that violate their freedom of religion," said Justin Lee, executive director of the Gay Christian Network, a nonprofit that provides support for gay Christians and their friends and families and encourages churches to be more welcoming.
"If anyone tried to force a church to perform a ceremony against their will, I would be the first person to stand up in that church's defense."
Thirteen states and the District of Columbia now recognize gay marriage.
Some Christian denominations, such as the United Church of Christ and the Unitarian Universalist Association of Congregations, accept gay marriage. The Episcopal Church recently approved a blessing for same-sex couples, but each bishop must decide whether to allow the ceremony in his or her local diocese.
The majority of Christian denominations, however, view homosexual relationships as sinful. In more hierarchical denominations, like the Roman Catholic Church or the United Methodist Church, individual churches are bound by the policies of the larger denomination. But nondenominational churches and those loosely affiliated with more established groups often individually decide how to address social issues such as gay marriage.
Eric Rassbach is an attorney with the Becket Fund for Religious Liberty, a public interest legal group that defends the free expression rights of all faiths. He said it is unlikely the government would try to force a pastor to perform a same-sex marriage, but churches that rent out their facilities to the general public could face problems if they refuse to rent to gay couples.
Although his organization has not advocated it, he said it could strengthen a church's legal position to adopt a statement explaining its beliefs about marriage.
"A number of groups don't have a written doctrine," Rassbach said. "Say a group like the Primitive Baptists — they don't want a written-down credo, but the courts like written-down things."
Rassbach said it was important for churches to get their beliefs in writing before a dispute arises, otherwise it can look to a court as if something was done after the fact as an attempt to cover up hostility to gays.
Airline Baptist Church Senior Pastor Chad Mills said members of the public use their facilities in Bossier City, La., for many activities, including Zumba classes. In the past, anyone who could pay the fee was allowed to reserve the space. But recently, the church changed its rental policy to allow wedding-related events only for male-female couples.
Some denominations are less concerned about the Supreme Court rulings. The Assemblies of God, the group of churches comprising the world's largest Pentecostal denomination, sought legal advice after the rulings. An attorney for the group distributed a memo to ministers saying there was no reason to change their bylaws.
However, the memo also said that "doing so is not inappropriate, and may be warranted based on future rulings by the Supreme Court and other state and federal courts."
The bylaw changes are coming at a time when many churches are wrestling with gay marriage in general and are working hard to be more welcoming to gays and lesbians.
"It's probably one of the most difficult issues our churches are facing right now," said Doug Anderson, a national coordinator with the evangelical Vineyard Church. "It's almost an impossible situation to reconcile what's going on in our culture, and our whole theology of welcoming and loving people, versus what it says in the Bible."