Lambda Legal and the ACLU filed a lawsuit Thursday on behalf of six gay couples asking for equal marriage-like rights in Hawaii.

Lambda Legal and the American Civil Liberties Union of Hawaii (ACLU) threatened it would file the lawsuit if Governor Linda Lingle vetoed a civil unions bill for gay couples. Lingle rejected the bill on July 6.

Jennifer C. Pizer, national marriage project director for Lambda Legal, said Lingle's veto was “a sad surrender to political expediency that does not support business or family interests, but damages them.”

The groups are returning to court after winning a landmark 1993 Hawaii Supreme Court case that struck down a law that limited marriage to heterosexual couples. But in approving the nation's first constitutional amendment that defines marriage as a heterosexual union, voters overturned the decision in 1998.

The amendment, however, left the door open for other forms of legal recognition for gay and lesbian couples, something gay activists have since urged lawmakers to act on.

The new lawsuit seeks the benefits and responsibilities of marriage for gay couples without asking the court for the titles of “marriage” or “civil unions.” The groups say the Hawaii Constitution prohibits sex discrimination.

Speaking to the AP, Garret Hashimoto, chairman of the Hawaii Christian Coalition, a group that strongly opposed the civil unions measure, said gay activists calling the right to marry a civil right is insulting.

He said legal recognition of gay unions was not about rights but sex: “It's behavior. It's not different than smokers or drinkers.”

Pizer said her group would drop the lawsuit if the next governor – Lingle is term-limited – signs a civil unions law.

The case is expected to reach the Hawaii Supreme Court.