LINCOLN, Neb. - Nebraska's unique constitutional ban on same-sex marriages was challenged by a federal court lawsuit that says the measure violates the rights of gay couples.

The constitutional amendment, adopted in 2000 after approval by 70 percent of the voters, prevents homosexuals who work for the state or the University of Nebraska system from sharing health insurance and other benefits with their partners.

Thirty-four states have so-called "Defense of Marriage" laws, but Nebraska is the only state whose constitution bans same-sex couples from enjoying many of the legal protections that heterosexual couples enjoy, the American Civil Liberties Union 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 ACLU said.

The ban was spearheaded the Nebraska Coalition for the Protection of Marriage, which was co-chaired by former Republican Gov. Kay Orr. It 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," council member Al Riskowski said of the lawsuit. "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 said 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."