The nation’s last unchallenged state same-sex marriage ban is about to lose that status.

“There will be a case filed challenging North Dakota’s same-sex marriage ban,” says Joshua Newville, a Minneapolis-based civil rights attorney who filed a suit Thursday against South Dakota’s ban on behalf of same-sex couples there.

Newville is in talks with advocates and attorneys in North Dakota and confirmed that either he or another attorney will bring a lawsuit against that state’s ban within six to eight weeks.

Until Wednesday, just three of the 33 states that ban same-sex marriage had not been sued over those policies. But same-sex couples sued Montana that day and South Dakota on Thursday, leaving only North Dakota’s unchallenged.

The same-sex marriage movement has enjoyed a streak of more than a dozen victories in federal courts since a pivotal Supreme Court decision last summer, striking down a central part of the Defense of Marriage Act and granting federal recognition to same-sex married couples. Since then, no state ban has survived a court challenge, according to the Human Rights Campaign, which advocates for same-sex marriage.

The latest two federal decisions, overturning bans in Oregon and Pennsylvania, were delivered last week with officials in both states saying they would not appeal those decisions. Same-sex couples are now allowed to legally marry in 19 states. More than 2 in 5 Americans live in such states, according to HRC.

Nancy Rosenbrahn, 68, hopes to be among them soon. She and her partner Jennie Rosenbrahn, 72, are the lead plaintiffs in the suit filed by Newville over South Dakota’s ban.

The road to taking on that prohibition began last summer. The two wondered what the Supreme Court’s DOMA ruling would mean for their own state’s constitutional ban, passed in 2006 by a 52 percent to 48 percent vote.

Then, after the Obama administration announced in February that it would no longer defend federal laws banning recognition of same-sex marriages, Nancy, whose last name then was Robrahn, decided it was time. She proposed to Jennie, whose last name at the time was Rosenkranz, and on April 26, after 27 years together, each said “I do.”

“I thought I would go to my grave never hearing that,” Nancy said. The wedding took place in Minneapolis and was officiated by Mayor Betsy Hodges. The two changed their last names to Rosenbrahn because, Nancy said, there wasn’t enough space on an official form for a hyphenated name.

She and Jennie were motivated to act because they felt their state should be part of the national movement to legalize same-sex marriage and they felt better protected than others to be a part of the challenge. South Dakota is among 29 states that lack an explicit ban on discrimination based on sexual orientation, according to the Human Rights Campaign. But because the pair own their home and a mobile-home business, they didn’t have to worry about any kind of retaliation from an employer or landlord.

North Dakota similarly lacks explicit protections from discrimination based on sexual orientation, a reality Newville has made clear to couples expressing interest in taking on that state’s constitutional ban on same-sex marriage, which was passed in 2004 in a 73 percent to 27 percent vote.

That lack of protection from discrimination represents one of the next battles in the fight for gay rights, Rosenbrahn says. ”Marriage was the start, but it’s not the end.”

In all, 29 state constitutions and four state laws limit marriage to heterosexual couples, according to a list maintained by the National Conference of State Legislatures. Several of those bans have been ruled unconstitutional in federal court, with some same-sex marriages allowed to proceed even as states appeal those decisions. Some same-sex marriage advocates hope to use the state-by-state fight to secure a Supreme Court ruling in their favor.

Much has changed since DOMA was enacted in 1996. Just 27 percent of respondents to Gallup and Pew polls that year supported same-sex marriage. Support has since doubled. Pew now reports support of 54 percent while Gallup reports 55 percent support.