State Sen. Mark Leno (D-San Francisco) said his SB1140 addresses the legitimate concerns from clergy that they could be forced to perform same-sex marriages that contradict their religious beliefs.
The bill passed the Assembly on Thursday, sending it to the Senate. Most Republicans opposed it.
Voters declared gay marriage illegal in California with Proposition 8 in 2008, but Leno's bill would apply if gay marriage were legalized in the future.
Leno says he wants to make it clear that the First Amendment right to freedom of religion includes the freedom not to perform gay marriage.
The Associated Press contributed to this report.