MADISON, Wis. - Wisconsin's gay marriage ban denies same-sex couples legal protections and serves no legitimate government purpose, the American Civil Liberties Union argued Monday in a brief asking a federal appeals court to preserve a ruling that struck down the prohibition.

The ACLU brought a lawsuit earlier this year on behalf of eight gay couples alleging the ban is unconstitutional. U.S. District Judge Barbara Crabb sided with the ACLU earlier this summer and ended the prohibition.

State attorneys under the direction of Republican Attorney General J.B. Van Hollen have asked the 7th Circuit Court of Appeals to reverse Crabb's ruling. The court has consolidated the case with a similar appeal from Indiana state attorneys; oral arguments are set for Aug. 26 in Chicago.

"By withholding from them the respect, recognition, and support that only marriage confers, Wisconsin stigmatizes these couples and their families as unworthy of the opportunity to express and legally embody their commitment in the most profound way that society provides," ACLU attorneys wrote in their brief.

Wisconsin voters amended the state constitution in 2006 to ban gay marriage or anything substantially similar. Wisconsin offers a domestic registry - which the state Supreme Court upheld as valid last week - that affords same-sex couples who join it a host of legal protections but gay couples contend the rights are limited.