Nine same-sex couples have filed a lawsuit in Denver District Court seeking to overturn Colorado’s constitutional ban on gay marriage.

The lawsuit is the latest of several filed in states across the nation challenging gay marriage bans, including Utah’s and Oklahoma’s that are currently before the U.S. 10th Circuit Court of Appeals in Denver. The issue is likely to culminate in a Supreme Court review.

The lawsuit, filed Wednesday, names Gov. John Hickenlooper and Denver City Clerk Debra Johnson as defendants.

Colorado permits civil unions between gay couples, but the state constitution bans gay marriage.

“This denial of equal protection, due process and basic fairness violates the Constitution of the United States of America,” says the lawsuit filed by the law firms of Reilly Pozner, Law of the Rockies and Gutterman Griffiths.

Although attorneys general from some states have declined to defend against similar lawsuits challenging same-sex marriage bans, Colorado Attorney General John Suthers said his obligations are clear.

“It is the job of the Attorney General’s Office to defend our state laws, and we will defend against this new lawsuit as we would any other,” he said.

Hickenlooper said in a statement that “as a matter of constitutional law, we appreciate that the courts will take it up. On the underlying question of equal rights, we believe Colorado made a step forward when we passed bipartisan civil unions legislation last year.”

Johnson said she wanted to issue marriage licenses to same-sex couples but decided not to do so after giving it a great deal of thought.

“I believe all adults should be able to marry the person they love regardless of sexual orientation; however, as an elected official, under oath I am sworn to uphold the law as written, even when those laws are in direct conflict with my personal beliefs,” she said in a statement. “I have a lawful duty to administer laws and policies regardless of when they are contrary to my personal beliefs.”

Wednesday’s lawsuit was the second in Colorado to address gay marriage. In October, Rebecca Brinkman and Margaret Burd filed a case in Adams County.

The plaintiffs in the newer case include administrators, educators, a legal assistant and recruiter, a technical writer, a psychotherapist, an aerospace engineer, a volunteer and a police officer, the lawsuit says.

Four couples are raising children together.

The 10th Circuit Court of Appeals will review federal court decisions in Utah and Oklahoma that struck down constitutional bans against gay marriage in those states.

Five of the couples in the Colorado lawsuit — Tracey MacDermott and Heather Shockey; Wendy and Michelle Alfredsen; Tommy Craig and Joshua Wells; Jodi Lupien and Kathleen Porter; and Christopher Massey and James Davis — wish to get married, the lawsuit says.

“Colorado law creates two classes of citizens: those free to marry the person they love, and those denied that fundamental right,” the suit says. “Same-sex couples in Colorado are relegated to a second-class level of citizenship that denies their relationships the full panoply of rights enjoyed by married opposite-sex couples.”

The other four plaintiff couples — Amy Smart and Sandra Abbott; Kevin and Kyle Bemis; G. Kristian “Kris” and Nan McDaniel-Miccio; and Sara Knickerbocker and Jessica Ryann Peyton — are legally married same-sex couples, having wed in other states. But those marriages are not acknowledged in Colorado.

“Even same-sex couples who have been married in other states are stripped of their marital status when they enter the state of Colorado,” the suit says.

Five Colorado advocacy groups, including One Colorado and the American Civil Liberties Union of Colorado, expressed support for the lawsuit.

“Just like thousands of other loving, committed couples across Colorado, the courageous plaintiffs who brought forth today’s case simply want to take care of their families and make a lifelong promise to the person they love,” One Colorado executive director Dave Montez said in a statement.

Montez said there’s a difference between having a civil union or marriage license and feeling comfortable enough to put a picture of your spouse on your desk at work.

House Speaker Mark Ferrandino, who sponsored a 2013 bill that made civil unions legal, called the lawsuit another step toward full equality.

“When we passed civil unions, it was a step, and this is another step as we continue to fight for marriage equality. Both in Utah and in Oklahoma, courts struck down bans against marriage equality. I think we’ll see a similar outcome here in Colorado,” said Ferrandino, who is the state’s first openly gay House Speaker. “I’m really glad this lawsuit is going forward, and I’m optimistic we’ll see full marriage equality.”

Ferrandino notes an initiative to make legal same-sex marriage could be on the November 2016 ballot.

“The courts, however, are moving much faster than I think everyone expected,” Ferrandino said.

Rep. Frank McNulty, R-Highlands Ranch, called the lawsuit “manufactured.”

“This looks to upend an initiative passed by Coloradans, and it flies in the fairness and our system of law,” McNulty said. He was referring to Amendment 43, which was passed by voters in 2006 and prohibits same-sex couples from getting married.

As the former House Speaker, McNulty killed a civil unions bill in 2012, when the GOP controlled the chamber.

Kirk Mitchell: 303-954-1206, denverpost.com/coldcases or twitter.com/kmitchelldp