Six couples have filed a federal lawsuit challenging Colorado's ban on gay marriage.

According to 7News Denver, attorney Mari Newman, whose firm Killmer, Lane & Newman, LLP is representing the couples, called the case “a slam dunk.”

“It's not often that lawyers get to say that,” she said at a press conference. “But here the 10th Circuit has been absolutely clear.”

Last week, the appeals court upheld a lower court ruling striking down Utah's marriage ban. It is expected to rule this month in a similar case challenging Oklahoma's ban.

A majority (53%) of voters in 2006 approved Amendment 43, which defines marriage in the Colorado Constitution as a heterosexual union.

“Plaintiffs seek a declaration from this Court that Amendment 43 … violate[s] the Fourteenth Amendment of the United States Constitution, and a judgment to permanently enjoin the enforcement of Amendment 43 and any other Colorado statute that refuse to allow same-sex couples to marry within the state or to recognize the validity of out-of-state marriages of same-sex couples,” the complaint reads.

Arguments in a similar lawsuit were heard last month by Judge C. Scott Crabtree.