Seven same-sex couples are attempting to overturn North Dakota's ban on same-sex marriage.

A lawsuit filed Friday in U.S. District Court in Fargo lawsuit challenges the constitutionality of the state's ban on same sex marriage and the refusal by North Dakota to recognize same sex couples legally married in other states and jurisdictions.

North Dakota is the last state in the nation to be sued by couples seeking the right to marry in their home state.

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That means cases are currently pending in all 30 states with gay marriage bans. Judges have overturned several of those bans since the U.S. Supreme Court struck down part of the federal Defense of Marriage Act last year.

North Dakota attorney general's office said it had not yet seen the suit and was not commenting. The 2004 voter-approved constitutional ban on same-sex marriage was passed by 73 percent of voters.

The plaintiffs include David Hamilton and Bernie Erickson of Fargo, who were married in Canada. Hamilton said they considered the risk of retaliation before filing suit.

"We'll just have to take that as it comes I guess," Hamilton said. "We're just very matter of factly a couple and we just sort of live our lives as regular guys paying taxes and doting on our grandkids."

Rep. Joshua Boschee, D-Fargo, takes a phone call while working at his desk in the North Dakota House of Representatives in Bismarck, ND. on Tuesday, Jan. 8, 2013. Boschee is North Dakota's first openly gay lawmaker. Will Kincaid/AP

Hamilton said North Dakota's refusal to recognize his marriage meant extra work and expense filing taxes this year.

"The most recent example is that we are required to file jointly as a married couple on our federal tax return," he said. "But we're required to file separate returns in North Dakota which led to an awful lot of extra accountant fees this year trying to get it all sorted out."

North Dakota has no specific civil rights protections based on sexual orientation. But that should not affect the case in federal court, said Minneapolis Attorney Joshua Newville, who filed the suit.

"The argument that not allowing same sex couples to marry or not recognizing their marriages is a deprivation of their equal protection under the United States Constitution is not changed by North Dakota's failure to protect its gay and lesbian citizens," Newville said.

But Newville said he warned the couples who filed suit they could face workplace or housing discrimination because they are taking a public stand.

"I had to have a frank conversation with many of them about the implications of that including the lack of protections in housing and employment and talking about the kind of press attention that they might get," he said.

Six of the seven couples who filed suit were married in other jurisdictions.

Besides Hamilton and Erickson, five couples were married in other states. One couple unsuccessfully sought a marriage license in North Dakota.

Newville also represents six South Dakota couples challenging that state's ban on same sex marriage.

Legal experts said the North Dakota lawsuit is largely symbolic, but could carry more serious weight.

"It's symbolic but sometimes symbolism is important, right? I think it has real, practical, actual effects on people nationwide and in North Dakota," said Carl Tobias, a professor at the University of Richmond School of Law who studies constitutional law.

The lawsuit claims violations on three issues that are guaranteed in the 14th Amendment to the U.S. Constitution: equal protection, due process and right to travel.

Like the South Dakota lawsuit, the complaint seeks a declaration that the statute and constitutional bans are unconstitutional and asks that the state be prevented from enforcing the ban 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.

"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," it states, while saying the couples are subject to "an irreparable denial of their constitutional rights."

Josh Boschee, who became the state's first openly gay legislator in 2012, said he believes North Dakota is much different place than it was 10 years ago and the lawsuit demonstrates that the issue is common throughout the nation.

"I think it shows that there's agreement in all 50 states that current law is unfair to lesbian and gay families," said Boschee.

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

Before the lawsuit was filed, Tom Freier, executive director of the North Dakota Family Alliance, which campaigned to bring the measure to the North Dakota ballot in 2004, said any such challenge would face strong opposition.

The Associated Press contributed to this report.