BISMARCK, N.D. (AP) — A newly married lesbian couple is poised to become the first to challenge South Dakota's ban on same-sex marriage following the state's refusal to grant the women a name change after they were legally married in Minnesota.

The couple, Jenny and Nancy Rosenbrahn, plan to file the lawsuit next week in federal court, according to their attorney, Joshua Newville. The Minneapolis-based lawyer said Thursday he also has been talking with couples looking to file suit in North Dakota, which along with South Dakota and Montana are the only states with gay marriage bans that haven't been challenged in court, according to gay-rights advocacy group Human Rights Campaign.

"Our focus right now is to get filed in South Dakota and to focus on the case in front of us in the immediate short term," Newville said Thursday, but "we are very seriously contemplating filing in North Dakota."

The couple's Minnesota marriage license reads Jenny and Nacy Rosenbrahn, a last name that combines each of their original last names. But when Nancy Robrahn, 68, and Jennie Rosenkranz, 72, who live in Rapid City, went to the Pennington County courthouse to legally change their last names last week, they were denied.

That denial gave the women grounds to challenge a provision in federal law that allows states to not recognize same-sex marriages performed elsewhere, Newville said.

South Dakota Attorney General Marty Jackley's office didn't immediately return an after-hours phone message for comment Thursday. But Jackley has said he would defend the constitutional ban if a lawsuit were filed, noting that his responsibility as attorney general is to defend state laws.

Opponents of same-sex marriage said lawsuits in either state wouldn't be surprising, given what has happened around the country.

South Dakota voters narrowly approved the state's constitutional ban in 2006, with 52 percent of the vote. But North Dakota's ban was overwhelming approved by voters — passing with 73 percent of the vote — in 2004.

Tom Freier, executive director of the North Dakota Family Alliance, which campaigned to bring the measure to the ballot in 2004, said he suspected a North Dakota lawsuit would face a strong challenge.

"I think foundationally, the people of North Dakota are really strong in their beliefs on these sorts of issues," Freier said Thursday.

Mara Fogarty, a member of the Pride Collective and Community Center Board in Fargo, North Dakota, which provides resources for LGBT residents, said there's a lot of interest — and fear — in challenging the ban. She noted that under North Dakota's non-discrimination policy, sexual orientation and gender identity are not protected classes for matters such as housing and employment, "so a lot of people are afraid to stand up and make that happen."

"I know that people really, really are hopeful," she added. "It's a lot of hope, but not a lot of faith."