Six couples filed a federal lawsuit Thursday seeking to block South Dakota's gay marriage ban, leaving North Dakota as the only state in the country with an unchallenged law prohibiting same-sex weddings.

Greg Kabel

The lawsuit, filed in U.S. District Court in Sioux Falls, challenges a 1996 law passed by the Legislature and a voter-approved 2006 constitutional amendment banning gay marriage, which means such cases are now pending in 30 states with gay marriage bans. The lawsuit also challenges a U.S. provision allowing states not to recognize same-sex marriages performed elsewhere.

In 19 states and the District of Columbia, gay couples already can wed, with Oregon and Pennsylvania becoming the latest to join the list this week when federal judges struck down their bans and officials decided not to appeal.

South Dakota Attorney General Marty Jackley said he's obligated by law to defend the ban and that he believes that voters should decide whether same-sex couples should be able to marry. It's possible that the U.S. Supreme Court or another federal court could hear another state's lawsuit first, which would put South Dakota's case on hold, he said.

"We would be behind several other states," Jackley said.

He's among the defendants that also include Gov. Dennis Daugaard, Health Secretary Doneen Hollingsworth, Public Safety Secretary Trevor Jones, Pennington County Register of Deeds Donna Mayer and Brown County Register of Deeds Carol Sherman.

Five of the couples already got married in Iowa, Connecticut and Minnesota. The sixth couple was denied a marriage license Thursday, Newville said.

One of the plaintiffs, Nancy Rosenbrahn, of Rapid City, married her longtime partner in April in Minneapolis. They and some of the other couples in the lawsuit are planning a June 7 wedding reception.

"It's exciting, and for me it's a proud moment to be a part of changing history. And I feel the weight of that — that this is going to affect so many people beyond us," she said.

The lawsuit, filed by Minneapolis attorney Josh Newville, claims three violations that are guaranteed in the 14th Amendment to the U.S. Constitution: deprivation of equal protection, due process and right to travel.

"The State will incur little to no burden in allowing same-sex couples to marry and in recognizing the lawful marriages of same-sex couples from other jurisdictions on the same terms as different-sex couples, while the hardship to Plaintiffs of being denied due process, equal protection, and privileges or immunities is severe, subjecting them to an irreparable denial of their constitutional rights," it states.

The complaint seeks a declaration that the statute and constitutional bans are unconstitutional and asks that the defendants be prevented from enforcing the bans and be required to issue marriage licenses to same-sex couples and recognize gay marriages from other states. It also seeks reimbursement for lawyers and other costs.

State Rep. Steve Hickey, a Sioux Falls pastor who believes marriage should be restricted to a man and woman, said the legal challenge has been years in the making and was inevitable.

"Christian people ought not to point fingers at the decline in America because we've been a part of it," he said.

"This will probably get decided by one judge. One swing judge will decide this for 300 million people."

North Dakota voters in 2004 overwhelmingly passed a constitutional ban on same-sex marriage.

Newville said several couples from North Dakota have contacted him about possibly representing them for a legal challenge in that state, which he's seriously considering.

"What seemed doubtful just a few weeks ago seems possible now," said Mara Morken Fogarty, a board member of the Pride Collective and Community Center, which provides resources to LGBT people in the Fargo-Moorhead area. Morken Fogarty and her partner were married last August after Minnesota legalized same-sex marriage.

If a challenge is filed in North Dakota, it will be met with staunch opposition, said Tom Freier, the executive director of the North Dakota Family Alliance, which campaigned to bring the measure to the North Dakota ballot in 2004.

"We are very comfortable and confident that the constitutional amendment we have should stand and if for some reason it wouldn't, I'm very comfortable that our attorney general would appeal that," he said.

Karyn Hippen, the mayor of Thompson, North Dakota, is that state's first mayor to join a national coalition of mayors who support same-sex marriage. Although 73 percent of the voters favored the constitutional ban, Hippen said she believes there is support in the state for allowing same-sex marriage.