NEW ORLEANS (AP) — A gay couple in New Orleans is suing over being denied a marriage license in Louisiana, claiming their rights are being violated by a state constitutional ban of same-sex marriage.

Kristoffer Bonilla, 33, and John Thomas Wray, 18, are asking a federal judge to strike down the constitutional amendment, which lawmakers and voters overwhelmingly approved in 2004.

The men filed the lawsuit against several state and local officials on April 2, the same day they said they were denied a marriage license. It claims the state’s marriage amendment violates the First Amendment ‘‘by curtailing the right to marry based upon a religious interpretation of the nature and purpose of marriage itself.’’

‘‘By failing to articulate a legitimate, compelling and secular interest for the restriction on marriage, the state has necessarily established a wholly religious civil institution,’’ it says.

Bonilla, who said he graduated from a New Orleans law school but isn’t a practicing attorney, drafted the lawsuit before they applied for the license.

‘‘We were hoping for the best but prepared for the worst,’’ he said in a telephone interview Tuesday.

Health and Hospitals Secretary Alan Levine, who is named as a defendant, said he believes this is the first case of its kind in Louisiana.

Advocates on both sides of the issue also said they weren’t aware of another case like it in the state.

‘‘This has the potential to be a pretty important case,’’ said Levine, who received a copy of the lawsuit on Monday.

Four states, Massachusetts, Connecticut and most recently Vermont and Iowa allow gay marriage. Twenty-nine states ban same-sex unions, including California, which approved Proposition 8 in November with 52 percent of the vote.

In Louisiana, after 78 percent of voters approved the ‘‘Defense of Marriage’’ amendment, a state district judge struck it down because it violated another provision of the state constitution — the requirement that an amendment cover only one subject. In January 2005, however, the Louisiana Supreme Court reversed that ruling and reinstated the amendment.

Levine said the state — both lawmakers and voters — was definitive in its stance against gay marriage and will defend that position in court.

‘‘There’s no argument. The law is crystal clear in Louisiana,’’ he added.

Randy Evans, an attorney for Forum for Equality, which had challenged the amendment, said the case decided by the state Supreme Court in 2005 didn’t delve into any federal constitutional issues.

‘‘The earlier case really has no controlling effect on this lawsuit,’’ he said.

Alliance Defense Fund attorney Mike Johnson, who argued for the amendment when the Supreme Court heard the case, called the new lawsuit frivolous.

‘‘Our marriage amendment is comprehensive in its scope and definitive in its meaning, and there’s no question that our state Supreme Court has upheld it,’’ he said.

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Associated Press writer Melinda Deslatte in Baton Rouge, La., contributed to this report.