SACRAMENTO, Calif.  —  A California law granting domestic partners (search) nearly identical legal rights as married couples does not conflict with a voter-approved ban on gay marriage (search), a state appeals court ruled.

California's domestic partner law represents the nation's most sweeping recognition of domestic partner rights short of Massachusetts, where gay marriage is legalized, and Vermont, which recognizes civil unions (search) for gay couples. It grants registered couples virtually every spousal right under state law except the ability to file joint income taxes.

The 3rd District Court of Appeal said Monday that the law did not undermine Proposition 22 (search), the 2000 initiative that defined marriage as between a man and a woman. That measure was "intended only to limit the status of marriage to heterosexual couples and to prevent the recognition in California of homosexual marriages," the three-judge panel said.

The ruling upheld a trial judge's decision in favor of the domestic partner law, which was signed by former Gov. Gray Davis (search). There are now about 29,000 couples registered as domestic partners, according to the secretary of state's office.

The Campaign for California Families (search) had challenged the domestic partner law. Randy Thomasson, executive of the Campaign for California Families, said the group would appeal and move for another ballot initiative that would end domestic partnerships.

"This ruling gives impetus to the push for a constitutional amendment to protect marriage from the clutches of judges and politicians," Thomasson said.

But Jenny Pizer, senior counsel for the Lambda Legal Defense and Education Fund (search), a pro-gay rights group, said the ruling "confirms the common-sense understanding that people in California have that domestic partnership and marriage are different."

Last month, a San Francisco County Superior Court judge ruled that laws limiting marriage to one man and one woman were unconstitutional, as was Proposition 22.

The ruling was appealed and will likely go to the California Supreme Court. Gov. Arnold Schwarzenegger (search) has said he opposes gay marriage but would not try to amend the state constitution if the Supreme Court upholds the lower court ruling.