As the dominos continue to fall, another state's ban on marriage equality ban has been lined up for the execution block. South Dakota has become another state with an active case against the constitutional amendment banning same-sex marriage.

On Thursday, six couples filed a federal lawsuit seeking to block the state's ban on same-sex marriage. This development leaves only South Dakota's sister to the north as the only state without an case against that state's ban, according to The Associated Press.

The ban passed in 2006 via referendum; however, following the onslaught of liberty crushing the ban in many states, the couples saw it as an adventitious sign to file the case now. The AP reports that the lawsuit was filed in the U.S. District Court in Sioux Falls and will also be challenging the state's ban on recognizing out of state same-sex marriages.

Marty Jackley, South Dakota's attorney general, has stated it is his duty to protect the ban in the courts. He also believes that the state's residents should decide on the rights of the minority. Among the defendants are also Gov. Dennis Daugaard, Health Secretary Doneen Hollingsworth, Public Safety Secretary Trevor Jones, Pennington County Register of Deeds Donna Mayer and Brown County Register of Deeds Carol Sherman, according to the AP.

Five of the couples already married in Iowa, Connecticut and Minnesota; however, the sixth couple was denied a marriage license Thursday, their attorney Josh Newville said.

North Dakota may not be left alone for long. According to PolicyMic, Newville is considering filing a lawsuit in North Dakota. The ban was passed in 2004 also via a referendum vote with 75 percent of voters in favor of it. However, the last state may be the hardest. PolicyMic said that a Gallup Poll of 2012 shows that North Dakota has the smallest LGBT community proportional to the population: 1.7 percent.

There are currently 19 states with marriage equality, including the District of Columbia.