U.S. District Judge Martin Feldman upheld Louisiana’s ban on same-sex marriage Wednesday, the first time a federal judge has ruled against marriage equality proponents since the U.S. Supreme Court’s landmark ruling last year in U.S. v. Windsor invalidated a portion of the federal Defense of Marriage Act.

In his long-awaited 32-page decision, Feldman dismissed a lawsuit brought by same-sex marriage proponents who argued that Louisiana’s ban violates the U.S. Constitution’s guarantee of equal protection under the law, writing that Louisiana has a “legitimate interest” in “addressing the meaning of marriage through the democratic process.”

It marked the first time since the Windsor ruling that a federal judge has decided a state’s authority to define marriage trumps the right of a gay or lesbian couple to equal treatment, snapping an unbroken string of victories for gay-rights advocates in states from Utah to Virginia.

But Feldman’s decision is not the end of the legal struggle over gay marriage in Louisiana. The plaintiffs in the lawsuit, led by the Forum for Equality Louisiana, announced immediately that they would appeal the decision to the 5th U.S. Circuit Court of Appeals.

And while the 5th Circuit has a reputation as one of the most conservative federal appeals courts, the issue of gay marriage could be taken up soon by the U.S. Supreme Court.

Judges in more than 20 states have struck down nearly identical marriage laws, in many cases drawing on the high court’s Windsor decision.

Already, two federal appeals courts — the 10th Circuit in Denver and the 4th Circuit in Richmond, Virginia — have backed such rulings. And a conflicting decision from the 5th Circuit, which also has a Texas case pending before it, could prompt a Supreme Court review.

In the meantime, those in favor of Louisiana’s ban on same-sex marriage hailed a victory on Wednesday, while gay-rights advocates vowed to continue fighting.

Gene Mills, head of the conservative Louisiana Family Forum, said, “This ruling confirms that the people of Louisiana — not the federal courts — have the constitutional right to decide how marriage is defined in this state.”

Dalton Courson, an attorney for the plaintiffs in the lawsuit, said, “We always anticipated a difficult fight to have same-sex marriages recognized in Louisiana,” adding, “We plan to carefully present our case to the appellate court.”

At a news conference in front of the federal court building in New Orleans, members of the Forum for Equality said they were planning to hold a rally Wednesday evening in Jackson Square.

Feldman’s ruling turned in large part on the question of whether Louisiana’s marriage laws violate the 14th Amendment to the Constitution by singling out one group of people — homosexual couples — for disparate treatment.

Supreme Court precedent suggests a state may enact such a law only if it “can be said to advance a legitimate government interest.”

The plaintiffs, including several gay and lesbian couples who have married in other states and wanted their marriages recognized in Louisiana, argued that no such governmental interest exists. And they asked Feldman to apply a strict standard known as “heightened scrutiny” in their case, noting that gay and lesbian couples historically have been the target of discrimination.

Under heightened scrutiny, Louisiana would have to prove its marriage laws not only serve a “legitimate” purpose but are “necessary to the accomplishment” of “a compelling governmental interest.”

Feldman — an appointee of President Ronald Reagan who is known as a generally conservative jurist — disagreed on both points. He opted against heightened scrutiny, saying that neither the Supreme Court nor the 5th Circuit has ever “defined sexual orientation as a protected class, despite opportunities to do so.”

And he cited the state’s argument that its marriage laws “serve a central state interest of linking children to an intact family formed by their biological parents.”

Even more critical, the judge wrote, the state has a legitimate “interest in safeguarding that fundamental social change, in this instance, is better cultivated through democratic consensus.”

Broadly speaking, Feldman sided with the state’s lawyers in his interpretation of the Supreme Court’s Windsor decision, breaking with nearly every other federal judge who has ruled in similar cases.

As in other lawsuits around the country, the plaintiffs hung their argument in part on Justice Anthony Kennedy’s majority opinion in that case. Kennedy said the federal government must recognize the marriage of a same-sex couple living in New York and other states where same-sex marriage is legal. Doing otherwise, he argued, would be tantamount to saying their marriages are “less worthy” than traditional ones.

But Feldman, as a few dissenting federal judges have done in the past few months, zeroed in on Kennedy’s lengthy discussion of federalism. He read Kennedy’s opinion as affirming the role of the states, rather than the federal government, in defining marriage.

Quoting directly from the Windsor decision, Feldman wrote, “The definition of marriage is the foundation of the state’s broader authority to regulate the subject of domestic relations.”