Nebraska's one-of-a-kind ban on same-sex marriages was challenged Wednesday in federal court by the American Civil Liberties Union (search) and three other groups.

The lawsuit says the ban, which was approved by voters in 2000 and added to the Nebraska Constitution the next year, violates the rights of gay and lesbian couples.

"No other state constitutionally prohibits state and local government officials from recognizing same-sex relationships in any way, including as domestic partnerships," according to the lawsuit, which was filed in U.S. District Court in Lincoln.

Thirty-four states have so-called "Defense of Marriage" laws, but Nebraska's ban is the only one that bans same-sex couples from enjoying many of the legal protections that heterosexual couples enjoy, the ACLU said.

"It singles out lesbian, gay and bisexual people," the ACLU said. "While different-sex couples may seek and obtain legislation and government employment policies that protect their domestic partnerships, same-sex couples are prevented from doing so."

The constitutional amendment, known as Initiative 416, passed with 70 percent of the vote. It prevents homosexuals who work for the state or the University of Nebraska system from sharing health insurance and other benefits with their partners.

The ACLU was joined in the lawsuit by Citizens for Equal Protection (search) and Nebraska Advocates for Justice and Equality (search).

The ACLU's Lesbian and Gay Project and the New York-based Lambda Legal Defense (search) and Education Fund (search) are underwriting the lawsuit.

"This is by far the most extreme anti-gay family law in the country," said Lambda attorney David Buckel.

The ban prevents same-sex couples from "securing protection against a wide array of injuries that domestic partnership laws and policies are designed to address, including being prevented from visiting a same-sex partner in the hospital, making care decisions when a same-sex partner is incapacitated, taking bereavement leave when a same-sex partner dies, or making funeral arrangements for a same-sex partner after death," the lawsuit says.

The ban was spearheaded the Nebraska Coalition for the Protection of Marriage, which was co-chaired by former Republican Gov. Kay Orr. The coalition includes the Mormon church, the Nebraska Catholic Conference and Family First.

The ban also was supported by the Nebraska Family Council, a nonpartisan group that promotes "biblical values in Nebraska families, school and government."

"I believe the goal is to push the United States Supreme Court to ultimately redefine marriage," said council member Al Riskowski. "The definition of marriage is between one man and one woman. They'd like to see it go beyond that."

Same-sex marriages are recognized by 11 states and thousands of companies and more than 150 local governments and agencies nationwide, according to the lawsuit.

The ACLU stressed that the lawsuit does not ask for recognition of same-sex marriages, civil unions or domestic partnerships. Instead, it seeks "nothing more — and nothing less — than a level playing field."