Defenders of traditional marriage plan to appeal Tuesday's ruling that declared a California ballot initiative defining marriage as between a man and a woman unconstitutional. This puts the Proposition 8 on track for likely consideration by the U.S. Supreme Court.

A three-judge panel of the 9th U.S. Circuit Court of Appeals ruled 2-1 that a lower court judge correctly interpreted the U.S. Constitution and Supreme Court precedents when he declared in 2010 that Proposition 8 violated the civil rights of gays and lesbians.

The ruling states that "although the Constitution permits communities to enact most laws they believe to be desirable, it requires that there be at least a legitimate reason for the passage of a law that treats different classes of people differently. There was no such reason that Proposition 8 could have been enacted."

Proponents of the initiative were not surprised with the ruling, but say the decision is an outlier: "The 9th Circuit's decision is completely out of step with every other federal appellate and Supreme Court decision in American history on the subject of marriage," said Andy Pugno, general counsel for ProtectMarriage.com. "Ever since the beginning of this case, we've known that the battle to preserve traditional marriage will ultimately be won or lost not here, but rather in the U.S. Supreme Court."

ProtectMarriage.com is deciding between appealing the case to a larger panel of the 9th Circuit or going straight to the Supreme Court. In the meantime, same-sex marriages will not resume in the state until the deadline passes for an appeal.

California voters passed Proposition 8 with 52 percent of the vote in November 2008, five months after the state Supreme Court legalized same-sex marriage by striking down a pair of laws that had limited marriage to a man and a woman.

The ballot measure inserted the one man-one woman provision into the California Constitution, thereby overruling the court's decision.

The court crafted a narrow decision that applies only to California, even though the court has jurisdiction in nine western states. California is the only one of those states where the ability for gays to marry was granted then rescinded.

"Whether under the Constitution same-sex couples may ever be denied the right to marry, a right that has long been enjoyed by opposite-sex couples, is an important and highly controversial question," the court said. "We need not and do not answer the broader question in this case.

One legal analyst said the U.S. Supreme Court might not agree to take up the case on appeal because the appeals court focused its decision exclusively on California's ban.

"The ruling is on the narrowest ground possible," said University of Santa Clara constitutional law professor Margaret Russell.

The panel also said there was no evidence that former Chief U.S. Judge Vaughn Walker was biased and should have disclosed before he issued his decision that he was gay and in a long-term relationship with another man.

Pugno said that ultimately Tuesday's decision "disregards the will of more than 7 million Californians who voted to restore marriage as the unique union of only a man and the woman. We are confident that the rights of California voters will finally win out."

The Associated Press contributed to this report.