Two gay couples have joined a lawsuit which challenges New Mexico's laws limiting marriage to heterosexual couples.

Longtime partners A.D. Joplin and Greg Gomez and Monica Leaming and Cecilia Taulbee became plaintiffs last week in a lawsuit filed by the American Civil Liberties Union of New Mexico (ACLU-NM) on behalf of two gay couples in March.

“With this lawsuit, we are trying to have the courts confirm [that] the ability for same-sex couples to marry is already a protected right in New Mexico,” Micah McCoy, communications director for ACLU-NM, told Farmington daily The Daily Times.

New Mexico is the only state in the country that neither recognizes nor prohibits the recognition of gay couples. The New Mexico Constitution's definition of marriage makes no mention of gender. However, the state's application for a marriage license includes spaces to list the bride and the groom, terms New Mexico Attorney General Gary King has said are “gender specific.”

Leaming, 40, and Taulbee, 51, have been together for 15 years.

“I'm not in a fight, I just want to show everyone that I love Cecilia,” Leaming said.

The move comes after another gay couple filed a separate lawsuit last week.

(Related: Second New Mexico lawsuit seeks right to marry for gay couples.)