Five gay and lesbian couples on Monday filed a federal lawsuit challenging Alaska's ban on gay marriage.

Plaintiffs in the case are an unmarried couple and four couples who married in a state where such unions are legal.

Plaintiff couples argue that Alaska's 1998 voter-approved constitutional amendment limiting marriage to heterosexual couples violates the equal protection and due process clauses of the U.S. Constitution.

Married plaintiffs are Matthew Hamby and Christopher Shelden; Christina LaBorde and Susan Tow; Sean Egan and David Robinson; and Tracey Wiese and Katrina Cortez. Courtney Lamb and Stephanie Pearson are unmarried but wish to marry in Alaska.

Hamby, who married his husband in 2008 in Canada, said the lawsuit was important “because marriage should be available to all loving couples. It's important to us that our family is recognized by the State of Alaska and that we have the same rights and privileges as others.”

Earlier this year, Alaska Attorney General Michael Geraghty told the AP that he would defend the state's ban in court.

According to the Human Rights Campaign (HRC), only two states, Montana and North Dakota, remain without an active lawsuit challenging marriage equality bans. A challenge in South Dakota, which also doesn't have an active case, is being planned.