RAPID CITY, S.D. | South Dakota is now one of two states with a ban on same-sex marriage that hasn't been challenged in court.

Four gay couples announced Wednesday they are suing Montana over its constitutional ban on same-sex marriage. The lawsuit makes North Dakota and South Dakota the two remaining states in the country with same-sex marriage bans and no lawsuits challenging them.

Rapid City resident Nancy Rosenbrahn and her wife plan to file a lawsuit in the coming days challenging the state's constitutional ban on same-sex marriage. They will also contest a provision in federal law that allows states to not recognize same-sex marriages performed elsewhere.

Rosenbrahn and her wife married in Minnesota in April.

Rosenbrahn says the couple is seeking the "equality that everyone else has."