A federal judge in Utah struck down the state's gay marriage ban Friday in a decision that signals bans in other states could be threatened as well.

U.S. District Court Judge Robert J. Shelby struck down Utah's constitutional amendment banning gay marriage, saying it was a violation of the U.S. Constitution's due process and equal protection clauses.

This decision was the first ruling by a federal court on a state same-sex marriage ban since the U.S. Supreme Court struck down the Defense of Marriage Act in June in the case United States v. Windsor.

While the Supreme Court purposefully did not rule on state gay marriage bans, the Utah decision indicates that the Windsor decision could be interpreted as requiring them to be struck down across the country.

Shelby seized upon the dissent of Justice Antonin Scalia, a prominent conservative on the court, in which Scalia warned that the majority's logic in striking down DOMA — that DOMA was simply intended to harm gay people — would inevitably be used to strike down state bans across the country.

Now, Shelby is doing so. "The court agrees with Justice Scalia’s interpretation of Windsor and finds that the important federalism concerns at issue here are nevertheless insufficient to save a state-law prohibition that denies the Plaintiffs their rights to due process and equal protection under the law," Shelby writes.

Utah passed its amendment to the state constitution banning gay marriage with 66 percent of the vote in 2004. 

Shelby acknowledged that he was ruling against popular opinion. "The legal issues presented in this lawsuit do not depend on whether Utah’s laws were the result of its legislature or a referendum, or whether the laws passed by the widest or smallest of margins," he wrote. "The question presented here depends instead on the Constitution itself." 

The decision rejects Utah's argument that the ban is rooted in the tradition and history of heterosexual marriage. "Tradition and history are insufficient reasons to deny fundamental rights to an individual," Shelby wrote.

In a passage that runs counter to conservatives' interpretations of the Constitution, Shelby relies on an expansive view of the Constitution's protection of "liberty," and cites a Supreme Court case making that point in the context of abortion.

"The right to marry is an example of a fundamental right that is not mentioned explicitly in the text of the Constitution but is nevertheless protected by the guarantee of liberty under the Due Process Clause," Shelby writes.

The American Civil Liberties Union, a major backer of gay marriage rights, praised the decision. "Today’s decision is just another step in the amazing show of progress that we’ve seen in the past few years," said Joshua Block, staff attorney with the ACLU Lesbian Gay Bisexual and Transgender Project. "We will continue to work until all couples across the country have the freedom to marry."

The state of Utah can still appeal the decision, so it is not yet clear whether Utah will join sixteen states and the District of Columbia in allowing gay marriage.