Social conservatives are calling a California bill that would strengthen religious freedoms a backdoor bid to legalize gay marriage in the state.

Openly gay California Senator Mark Leno's Civil Marriage Religious Freedom Act has the support of gay groups, including Equality California, the state's largest gay rights advocate.

The bill would protect clergy from performing any civil marriage that is contrary to their faith.

“We are confident that same-sex couples will one day have the right to marry in California, and when that time comes this law will reassure faith leaders who have opposed marriage equality due to fears they would be compelled to perform marriages conflicting with their beliefs that state law, in fact, safeguards their religious freedoms,” Geoff Kors, executive director of Equality California, said.

“Although the U.S. and California Constitution protect freedom of religion, codifying these principles in state law will diminish any lingering ambiguity and will strengthen these vital freedoms,” he added.

Social conservatives, however, are opposed to the definitions used in the bill, including the distinction between civil and religious marriages.

“The concern is over the specific changing of the California statute to create a new class of civil marriage,” Everett Rice, legislative coordinator for the California Family Policy Council, a group that opposes gay rights, told the Christian-based Baptist Press.

“We are concerned that that's going to become another avenue of actually changing the definition of marriage itself. That's been pretty much the focus of Senator Leno's and those who support homosexual marriage. Our concern is that the bill incrementally begins the process of doing that. What we've seen in the past is that measures like these incrementally try to change whole institutions.”

The Alliance Defense Fund – a Christian-based legal group opposed to gay rights – called the bill a “Trojan horse.”

“Leno's bill is a Trojan horse that does nothing to protect religious institutions or other agencies of the church from being forced to violate their religious beliefs,” Mike Johnson, an ADF attorney, told the paper. “In fact, it further restricts church liberty and independence by giving the government greater power to define the church and its mission.”

The bill defines a civil marriage as a contract that requires a state-issued marriage license.